Q: Why did the chicken cross the Möbius strip?
A: To um, err, um ...
(according to what passes for mathematical humor (my favorite sub-genre), drawn from several sources but primarily from P. Renteln and A. Dundes in their paper "Sampling of Mathematical Folk Humor" in Notices of the American Mathematical Society, vol. 52, pp. 24-34, 2005)

Q: What sound does a drowning analytic number theorist make? A: log log log log...
(according to what passes for mathematical humor (my favorite sub-genre), drawn from several sources but primarily from P. Renteln and A. Dundes in their paper "Sampling of Mathematical Folk Humor" in Notices of the American Mathematical Society, vol. 52, pp. 24-34, 2005)

Q: What is lavender and commutes? A: An Abelian semigrape.
(according to what passes for mathematical humor (my favorite sub-genre), drawn from several sources but primarily from P. Renteln and A. Dundes in their paper "Sampling of Mathematical Folk Humor" in Notices of the American Mathematical Society, vol. 52, pp. 24-34, 2005)