Old one, but funny.
Three third-graders, a Jew, an Italian, and a Black kid are on the playground at recess. The Jewish kid suggests that they play a new game. "Let's see who has the largest dick," he says. "Okay," they all agree.
The Jewish kid pulls down his zipper and whips it out. "That's nothing," says the Italian kid. He whips his out. His is a couple of inches longer. Not to be outdone, the Black kid whips his out. It is far the biggest, dwarfing the other two in both length and width. The Jewish and Italian kid are stunned and amazed. "Wow, that thing is huge!" they exclaim.
That night, eating dinner at home, the Black kid's mother asks him what he did at school today.
"Oh, we worked on a science project, had a math test and read out loud from a new book ...and during recess, my friends and I played "Let's see who has the largest dick."
"What kind of game is that, honey?" says the mother.
"Well, me, Sidney and Anthony each pulled out our penises, and I had the biggest! The other kids say its because I'm black. Is that true, Mom?"
The mom replies: "No, honey. It's because you're twenty-three."