Browsing through the Wikipedia entry for mathematical jokes, I noticed a reference to the intriguingly titled Foolproof: A Sampling of Mathematical Folk Humor (pdf) that appeared in Notices of the American Mathematical Society back in 2004.
Many English-language mathematical jokes are based on word play involving standard mathematical concepts and terminology. In fact, many of the jokes involve food items, which may be a reflection of the fact that some mathematical concepts are hard to digest, or difficult to swallow:
Q: What’s purple and commutes?
A: An abelian grape.