Apparently when Uwe Rossler was a fan's favourite at Man. City the story went round that his dad/grandad flew the bomber that dropped bombs on Old Trafford in WWII. A T shirt was made of the event. Probably not that funny if one of your relatives had been affected by said raid as I believe Manchester suffered badly from bombing.
Never found Boardman funny at all, but that joke is genius.
Not because it is funny because it isn't.
The genius of it is that a mainstream club comic turns up on a prime time chat show with millions watching and tells a very risqué joke for those times, Des is wetting himself which in turn sets the audience off as well and next day everyone is talking about it, Boardman goes on to be a household name, makes millions, everybody still knows his name and the joke that he told and he has his very own thread on a football forum.
He struck a showbiz goldmine, and all because of a single joke.