“…The Aristocrats.”
Need context? Here’s the Wikipedia entry for the boundary-pushing comedy exercise known as The Aristocrats, a.k.a. “the world’s dirtiest joke”. If you want to see some of the best comedians’ take on it, here’s the definitive (and oh-so-very-not-safe-for-work) film on the joke: part 1, part 2, part 3, part 4, part 5, part 6, part 7, part 8, part 9.