You don’t have to be funny to give a great talk, but if you are, you can give a great and funny talk. So what’s the funniest scientific talk you’ve ever heard? Or the funniest joke or line?
Probably the funniest joke I’ve heard in a talk involved a bit of physical comedy. When I was in grad school, the Rutgers and Princeton ecology & evolution grad students had an annual symposium featuring talks from students from both schools. I remember a Princeton student (Josh Plotkin?) giving a theoretical talk on species-area curves. He was writing on blank overheads as he spoke, as theoreticians often did in those days (yes, I’ve now carbon-dated myself). He derived an expected form for the species-area curve, different from the traditional power-law form. Then he put up a pre-printed overhead comparing his predicted curve to real data. But after putting it up for a split-second–just long enough for the audience to see that the fit wasn’t great–he unfocused the projector, turning the whole image into a blur, and said “Now if you squint at this, you’ll see that the fit is actually pretty good!”
Dynamic Ecology 
Hard to remember the funniest talk I’ve been to, though Pej Rohani and Steve Ellner have certainly made me laugh. But for ecology textbooks, I think I have to nominate Hal Caswell’s Matrix Population Models. There are many fine footnotes, including this one:
In their excellent book on probability, Grimmett and Stirzaker (1992, p. 347) say that “The word ‘ergodic’ has several meanings, and probabilists tend to use it rather carelessly. We conform to this usage here.” I can only add that demographers are even more careless than probabilists, and that I will conform to the demographers’ usage here.
I remember sitting behind you and Peter Chesson at a Will Wilson talk where he did a Taylor series expansion and then turned to look right at you and Peter while saying “And now if you’re smart, you THROW OUT THE HIGHER ORDER TERMS…”, and you and Peter just smiling and shaking your heads “No”. It was really funny. But I may have been the only one in the audience besides you, Peter, and Will who got the joke.
Seb Diehl cracked the audience up once by showing a picture of a plankton tower hanging from the roof of a two-story building, and saying “The plankton towers would’ve been taller, but I’m only a very junior professor in the German system, so I don’t have a six-story building.”
Many years ago a visiting professor from Japan was presenting a seminar at the University of Michigan. He was introduced by the late George Nace, who spoke fluent Japanese. Nace informed the audience that the speaker would read his presentation in English, but, as the professor’s command of spoken English was very weak, any questions should be addressed to him, Nace, and he would translate the question and the answer. After the presentation there was a simple question that caused Nace and the professor to engage in a lengthy back and forth, all in Japanese. Of course no one in the audience had any idea of what was being said, but, in the middle of this conversation, a graduate student sitting in the back of the room shouted out: “Could you speak a little louder, please?”
When I was in grad school, two students gave a joke talk which started out apparently serious but was gradually revealed to be a roast of my supervisor, Peter Morin. I’m sure you had to be there to fully appreciate how funny it was. The talk was nominally about determinants of extinction risk in different taxa, and it was gradually revealed that Peter was a major cause of extinction in all the taxa he’d ever worked on. The students developed an elaborate model to explain extinction, the PMFLOO model (which stood for “Peter Morin something something…I can’t recall, unfortunately), which was illustrated with a ridiculously complex path diagram with a photo of Peter in the center. And whenever one of the speakers would say “PMFLOO”, the other would say “Bless you!”
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