this kind of explains it http://www.lnreview.co.uk/media/journal/001842.php
It makes you wonder whether you grew up in an especially potty-mouthed and anarchic playground. There was a similar non-joke shibboleth in mine, with the taboo sex replaced with racism:
Joke-teller: So this [insert racial slur of your choice] goes into the baker's, and asks for a loaf of bread. And the baker says "Brown or white?". And the [racial slur] says, "It doesn't matter - I'm on my bike."
At this point everyone except the mark laughs loud and long and waits for the mark to join in. At that moment, everyone should stop laughing:
Joke-teller: [to the mark] Why are you laughing? It's not a joke.
Abusing your trust (that a comedian will make you laugh and not wilfully waste your time) may be an acquired taste, but Penn (of ...and Teller) and Paul Provenza have said they've asked over 100 comics to do their own version. Provenza (currently working on the movie adaptation of Everybody poops)