Alright, another banjo joke that I didn't see at MIT:

A guy walks into a bar and orders a beer. Seeing an ad for a bluegrass band on the wall, he says to the bartender, "Did you hear the joke about the banjo player who..."
The bartender stops him, saying,"Wait a minute, buddy! I'M a banjo player. And my friend Lou, over there, he's a banjo player, too. And that big biker, Gus, by the door - he's a banjo player, too!"
The customer stops, saying,"Oh, well, never mind."
The bartender asks "Whatsa matter? Afraid to tell your banjo joke now?"
"No," says the customer, "I just don't want to have to explain it three times..."