Read this one today and it was kind of funny, but I modified it some for more 'punch'. Maybe another nerd will see the humor in it:
Dear Mr. Algebra,
Please stop asking us to find your X because if you don't know what or where she is then it means she isn't coming back and I don't want to know Y either.
Ah... I [kind of] get it JB. Nice play on the variables X and Y.
Anyways, I have a math joke that I heard from a friend:
"What do you get when you pour a root beer into a square cup? Just beer."