Old joke, new (realistic) ending
A duck walks into a bar...
Animal control is promptly called, the duck is then taken to a near by park and released.
What's the difference between Michael Jackson and a shopping bag?Many jokes are funny, I think (I didn't pay much attention to the pragmatics part of Ling 101), because they violate some Gricean maxim. For example, the maxim of manner says, in part, to avoid ambiguity. But ambiguity is precisely the thing that makes puns funny. The maxim of relation says to be relevant, but non sequiturs deliberately lead you one way and then make a totally irrelevant statement. But in jokes, this is totally acceptable, because we understand that Gricean maxims are often violated in jokes. They're not (necessarily) true, they're not (necessarily) brief, they're not (necessarily) relevant and they're not (necessarily) unambiguous. Perhaps there's a separate Gricean maxim that says when you're trying to tell a joke, ignore all the other maxims.
One is a famous singer songwriter facing charges of child molestation and the other's a shopping bag.
So when we come across "realistic" jokes where the beginning sounds like a joke and the "punchline" actually IS relevant, IS brief, IS unambiguous and IS true, it's kind of funny. Well to me, anyway. I'm overanalysing, aren't I? Stop reading this post and go read the "jokes". Have fun.