I found this article that talks a bit about mathematical folk humor. Essentially, there seem to be two types of math jokes: jokes about mathematics and jokes about mathematicians. In addition to eight variations of the “What’s purple and commutes?” (A: an abelian grape) joke that Kate presented in class, Renteln and Dundes give many more examples. I’ll highlight some of my favorites:
Q: What do you call a young eigensheep?
A: A lamb, duh!
Q: What do you get if you cross a mosquito with a mountain climber?
A: You can’t cross a vector with a scalar.
Q: Why can’t you grow wheat in Z/6Z?
A: It’s not a field.
A physicist and a mathematician are sitting in a faculty lounge. Suddenly, the coffee machine catches on fire. The physicist grabs a bucket and leaps toward the sink, fills the bucket with water, and puts out the fire. Second day, the same two sit in the same lounge. Again he coffee machine catches on fire. This time, the mathematician stands up, gets a bucket, and hands the bucket to the physicist, thus reducing the problem to a previously solved one.
Just a few more (not in the article but heard or read previously):
Q: What do you get if you divide the circumference of a jack-o-lantern by its diameter?
A: Pumpkin Pi.
Old mathematicians never die. They just lose some of their functions.
Q: What does a mathematician present to his fiancee when he wants to propose?
A: A polynomial ring!
Q: Why do you rarely find mathematicians spending time at the beach?
A: Because they have sine and cosine to get a tan and don’t need the sun!
So, are there really any funny math jokes? I’ll let you decide…