Hopefully, the start of a definitive list of things to avoid at all cost when speaking publicly.

Speaking in a monotone.

Failing to make eye contact with your audience.

Laughing nervously when you get a question.

Using light text on a dark background.

Slides that can't be read from across the room. Never, ever be able to say, "I guess you folks in the back might have some trouble reading the table, but..."

Would wearing sunglasses count? I saw this chemistry talk once, and this guy was wearing shades. It was the stupidest thing ever, and just really threw me off the rest of the talk.

What's wrong with light text on a dark background? It generally isn't my favorite, but I don't see that anything readable should be a problem.

Ooh ooh - these are good. "Laughing nervously" reminds me that laughing maniacally might also be a bad thing generally.

I don't actually have an issue with light text on dark background.

Along the lines of aggressive sweating. I think inappropriate bleeding might also be distracting.

Psychophysical studies have demonstrated that light text on a dark background requires more mental effort to read. With modern video projectors that are very bright, the lights in the room can stay bright, and thus black text on a pure white background is the easiest to read.

I'm surprise no-one has mentioned the speaker's cell phone going off. Very bad form.

Digging and scratching.

And no joke about the aggressive sweating. I had a prof for a grad seminar who sweat his way through each and every class meeting, and it was impossible to look away.

Packing heat.

Everything in shades of red and green with similar values. There's almost guaranteed to be at least one person with some degree of red-green colorblindness in the room. Also, avoid those pale shades of yellow and orange that look so clear on the laptop screen and so washed out on the projector.

Don't diss your own data. That's what the criticism is for, they don't need your help.

Fainting. Almost ended up there when I was pregnant and giving an hour-long talk during grad school--not advised.

Oh, and a bit more seriously--dry mouth/throat. Anytime I have to give talks that last more than about 20 minutes, I get dry, which sometimes makes me cough--so I always come prepared with fluids just in case the sponsor doesn't provide them.

Don't lose track of time. If you start getting excessively bogged down with lots of questions, graciously put them off until the end of the talk. Oh -- and you did time your talk well beforehand, right?

i also end up with a dry mouth before i speak. but sweaty palms. now if only i could switch those two, i'd be fine.

and hey, i LIKE comic sans font. you are such a party pooper!

Uncontrolled respiratory symptoms (sneezing, sniveling, coughing, etc).

This can backfire, though. I was once inveigled into giving a talk while suffering from a major headcold. There was no way I would stand up there sniveling, so I was doped to the gills with an antihistamine. I even took lots of questions. My colleagues told me afterward that I'd done a good job, but I had absolutely NO memory of it even a day later. For all I know, I could've been spouting absolute nonsense in front of customers.

Absentmindedly popping out your false teeth. (Had an English teacher in high school who did this, but in his case it might have been intentional.)

I expect removing your glass eye or repositioning your hairpiece would be similarly distracting.

Avoid unnecessary use of color.

If you have a bar graph comparing Treatment A with Treatment B, label them A and B, and use black figures on white ground. There is no point adding coloring and a color legend, unless the point is to show your section has a color printer, so nyah-nyah-nyah to everybody else.

When color is needed, make sure the palette you use does not have colors that will be ambiguous up on the screen. And avoid saturation. We need bright colors in traffic control lights, but you'll notice all the scenery around is in softened colors.

[fade in]
[typewriter effect]
Excessive animations and slide transitions.
[swirl out]
Just because powerpoint
[blink]
*can*
[stop blinking]
[swoop]
swoop,
[swirl]
swirl or
[bouce]
bounce every letter and
[swirl in a LOLcat image]
image doesn't mean you
[blink]
*have*
[stop blinking]
to use that feature.
[fade out]
[rolling credits]
See how annoying that is?
[sound effect]
[fade in]
I did use the rolling credits recently, but for the credits of a talk that didn't fit on one screen, so I like to think it was actually appropriate.
[fade out]

What about "don't be boring"? Someone already mentioned avoiding monotone speech, which is definitely in the same vein. How hard is it to have at least one slide that inserts some levity? You could have an indecipherable accent and a boring project and still pull out at least one or two entertaining moments.

Serif fonts.

No pants

Don't read your slides to people. Slides are there to support your talk, and unless you are talking to the illiterate, they don't need it read for them. This is by far the most annoying, and most common, mistake I see in presentations.

In a similar vein, do not put too much text into your slides or use them as a script of what your going to say.

UM.....Umm.....Ummm...

Seriously, though, the worst talk I ever went to was some guy who simply put up his PAPER and read chunks out of that. In a monotone. In a dark room. At least Powerpoint is more visually interesting.

The second worst talk was a woman who looked like she'd prepared her overheads 2 minutes before the talk and the commenced to draw random shapes all over that were supposed to represent what she was talking about. It was like deciphering hieroglyphics. She was talking so fast that you could barely keep up with her.

If you can do something midway between those two, I think you'll survive.

Drinking water and crunching on ice while next to a microphone. I'd say this is a hypothetical, but I really saw this happen (RFK Jr was the speaker)

The world needs all of these made into a movie.

If your presentation is projected directly from a computer use a standard cursor set, not cutesy ones like little winged pigs.

If you are a 13-year-old boy asked to give a book report in front of the class, do not have a raging, uncontrollable erection.

If you are an older male professor currently taking medication for erectile dysfunction, same deal.

1. as someone mentioned, time your talk. even if you're the frikkin dean of harvard. i HATE speakers who go overtime (cutting down beer drinking time), or skip the last 5 crucial data slides because their session is running overtime and the chairperson is dinging because they need beer too. HATE is not too strong a word.

2. fidgeting / tapping a pen or laser pointer on the lecturn / desk (old bad habit of mine, since cured).

3. laser pointers with fading batteries. the new green lasers look very cool btw. perhaps a bit flashy unless you're a senior postdoc at least ;) also excessive waving of said laser pointer (i might be slightly guilty of this last one...).

4. i don't mind light text on dark slides, especially if there'll be a lot of immunofluorescence pics that require the lights to be dimmed. a pure white background makes my eyes hurt.

5. spelling mistakes.

6. reading slides can actually be helpful if english is your second language, but a slide full of text is generally unhelpful.

7. keynote ftw.

Slides. Everyone ought to try doing a speech without slides once in a while. Did you know that most of the greatest speeches in history were done without slides? And, that almost none of the greatest speeches in history were done with slides? (Except perhaps Hans Rossling) Draw your own conclusions from this.

If you do have slides, either they should be a few words or some memorable pictures. Unless you want people to be reading your slides instead of listening to you.

Also, don't read your slides to the audience, unless you are trying to tell them they don't know how to read themselves.

Too many slides. (I.e., more than a handful) Have you ever seen a preso that wouldn't be improved by a few less slides?

Too much animation (mentioned above) -- which in my view is pretty much any animation at all

Repeating yourself too much, by saying the same thing over and over again which the audience has already heard, even if you have to come up with something to fill up some time.

The standard model -- say what you're going to say, say what you say, and say what you said. In other words, bore everyone, let them know how bored they are, and explain why they've been so bored. If you want to engage the audience help them reach their own conclusions

Talk really really fast without any pauses

Being full of yourself

Repeating yourself, again and again, by going back over what you've already said. (As you can tell, I'm well experienced with this approach, in fact, I've always said, if something's worth saying once, it's worth saying 426 times or so)

"Would wearing sunglasses count? I saw this chemistry talk once, and this guy was wearing shades. It was the stupidest thing ever, and just really threw me off the rest of the talk."

Was he blind or have some sort of eye condition? I think an acception could be made then. If that was not the case, that does sound stupid.

I almost always choose to use white text on a black background because I think it aids contrast and clarity. I actually hate seeing a white background in projected slides... most projector hardware and presentation rooms just can't handle it.

If you are using slides, either make sure that you've got the preview feature active on your laptop, or have (and can see) a list of the slides.

That might help you avoid the dreaded ("oops, I almost forgot to mention"/"Oh, what do you know, that point was on the next slide, so let me repeat it") combination.

Oh, and I almost forgot:

Due try too remember that the spell checker will knot flag you if ewe are using the wrong word.

+U Rnt 2 uz txtN tlk n yr slides, evr.

Excessive name dropping.

Reading directly from slides, and highlighting every word read with the laser pointer like it's a karaoke session.

Sweeping the green laser pointer across the audience as you turn around.

It's always best to avoid public speaking at all, unless you have been trained in doing it.

Granted, that may be impossible, so here are a few other things to avoid:

Propeller beanies, lederhosen, silly neckwear, or other odd attire.

Poorly written, badly organized presentations.

Musical accompaniment.

Racial slurs or references to "cripples" or "retards."

Leering at the opposite sex.

Religion.

Politics.

Please note: any of these need not be avoided if you are a celebrity or are running for public office. You'll have publicists to fix everything up.

Most of these points have already been covered, but are worth repeating.

Undersized typefaces. PowerPoint's default font sizes are there for a reason. (This sin is often committed by people who are trying to cram too much text into a slide.)

Gratuitous animation. This includes anything involving moving text as well as most transition effects. The "Appear" effect has legitimate uses, as long as it's used sparingly and not just in an effort to simulate the old "viewgraph striptease" effect (those of you who have been in the field for at least a decade know what I mean by that).

Spreading out your conclusions over multiple slides. When you put up a slide marked "Summary" or "Conclusions" I assume that that is your last slide. If you can't fit the basic conclusion into one slide, you are trying to cover too much ground for a typical 10-15 minute conference talk. A related sin: We don't need to see "Thank You" on a slide by itself.

Reading your slides. If you are giving a talk in something other than your native language, or you lack extemporaneous speaking skills, have your talk written out on paper and read from that instead.

Nose-picking. Saw a high-profile scientist do this at a major talk - all memory of slide content went out the window, no one talked about anything else but the nose. Uggh!

Talking at the screen. If you keep your feet pointed at the audience, this doesn't happen...

From my college days:

If you are running a presentation from your computer, change your background to something that is safe to show in public, just in case Powerpoint crashes.

If you aren't running from your computer, make sure to have the presentation on the presentation computer more than 2 minutes before your presentation. Realistically, you should test the presentation laptop to ensure everything works like you think it will.

Have a printout of your presentation, with enough copies of graphs for everyone. In the unlikely case something causes the laptop or projector to fail, you can still give a talk that covers your proper points, and the audience can see the important part of your visual component.

My suggestions:

Stay away from excessive "um"-ing and "like"-ing. Every word should be meaningful and relevant to your talk.

Don't put too much text on your slides. I use just a few key words to jog my memory if I get stuck. You want your audience to listen to what you are saying.

Eye contact and tone of voice are important if you want to hold attention. I try to maintain a rather conversational tone, especially when covering what may be considered dry subject matter. Try to look everyone in the room in the eye at least once. Not in one motion, though; that's just weird.

I put at least one image on each slide, and I think carefully about the placement to ensure things are visually interesting. It makes me happy. I recently got to have some fun with random stock photos of mad scientists. Woo! :)

Look nice-- not trying-too-hard-nice, but do look in the mirror before you leave the house in the morning. And for chrissakes, wear clothing that fits you. I have seen too many people dressed like small children headed to church. Gentlemen, don't wear a suit jacket unless it looks right. Or I'll be laughing at you on the inside the entire time.

Know your audience. Don't assume things. Figure out what background they are going to need to understand your message. And don't talk down to folks. You are a peer, relaying information everyone was simply unaware of before you started speaking.

Drop the timidity. Own everything you say.

A tiny, tiny bit of self-deprecation can be humanizing. Today I talked about an EPA method I learned this summer-- something I didn't get right the first time. The slide title read "Samia's DOC: The Epic Saga."

Practice, practice, practice. Time yourself and get a feel for the flow of your talk. Enough repetition, and you'll know exactly which key points to include when it's time to get up there.

I almost forgot: please employ more than one facial expression during the course of your ten to fifteen minutes. I hate when people's faces turn to wax up there. It's disconcerting.

HAVE A POINT, A THESIS, AN ARGUMENT!!! This goes for you, too, tenured Professor who yammers on and on for 20 minutes and never gets to the point.

And, I second the point someone raised above with regards to NOT using slides. I have asked students in various courses that I have taught what they're feelings were about power point vs. say, one concise overhead. While the majority of them said they preferred power point, when I pressed them about whether or not they took more or less notes with power point presentations, they admitted that they both absorbed more from the speaker who used an overhead and wrote way more notes.

Read: fancy slides do not a great orator make!

I actually like a bit of "unnecessary math". My point is of course that the most important thing is to know your audiance.

Then there's the other side: the confident extemporaneous speaker who gives a 30 minute lecture with 300 slides, while repeating for 9 of every 10 slides, "I'll just skip this one." Of course, moving through slides so quickly makes the presentation look like one of those pretentious, hand-held indie flicks.

HP said: "If you are a 13-year-old boy asked to give a book report in front of the class, do not have a raging, uncontrollable erection.
If you are an older male professor currently taking medication for erectile dysfunction, same deal."

Unless you are an older male professor giving a talk about erectile dysfunction drugs. Then you will become one of the funniest anecdotes in medical research.

I think perhaps the single most important thing, which you think would be obvious, is to know your subject matter and be comfortable talking about it. You get this way by talking about it. Discuss it with your lab mates, bring it up at parties, etc. So many scientists, and even students, work in a vacuum. It's easy to feel like you know perfectly well what's going on, but be unable to string together a coherent set of thoughts on the subject when forced to talk about it.

Not only does that make it easier to feel comfortable talking in public, it can also make a lot of other presentation problems go away: if you know the story you're telling, you'll read off your slides less, say "um" less, make eye contact, etc. And if you believe what you're saying and are excited about it, people will be more inclined to believe what you're saying and be excited about it, too.

Just a comment on slides: While I generally agree that light-on-dark text is harder to read than dark-on-light, if you have reasonable font sizes and limited text per slide, then that shouldn't be big deal. And the blinding effect of a light background in a darkroom can be really obnoxious. Yes, with the brightness of some projectors, you can leave the lights brighter and still read the text, but generally if you have photos or moderately complex figures, you need it pretty dark to see the details anyway.

I've seen lots and lots of presentations, and I can honestly say I really like the classic white/yellow and dark blue.

Scratching your body parts....probably not evolved completely to humans yet!