Most Underrated Math Joke Ever

I believe the following joke is the most underrated, because I was nearly booed off stage when I told it during a “Math Joke Hour” at the 2009 NCTM Annual Meeting in Washington, DC:

What’s the difference between a math PhD and a large pizza?
The pizza can feed a family of four.

But perhaps the most underappreciated is the following joke pair, which unfortunately can’t be told in many situations:

Did you hear about the constipated mathematician?
He worked it out with a pencil.

What kind of pencil?
A #2 pencil, of course.

Got some that you think deserve more credit but get less than either of these? I’d love to hear about them.