The Aristocrats

Does anyone know the joke called "The Aristocrats"? Penn Jillette of Penn and Teller and comedian Paul Provenza made a documentary of 101 comedians telling the joke in their own style.

George Carlin, Robin Williams, Whoopi Goldberg, Eric Idle, Gilbert Gottfried and (singled out as being most offensive) Bob Saget take turns telling it, which theoretically will provide insight to the creative process. (I have alerted Brad Thacker for an insider's pov.)

It's unrated (to avoid NC-17) due to language. Penn is advertising it with "No nudity. No violence. Unspeakable obscenity." No matter what they do, I'm sure some jackass will take his kids to see Mork and Whoopi and go screaming to the media.