Two country boys are sitting on the porch, along with a dog. The dog is licking his balls. One of the country boys says “I wish I could do that.” The other one says:
a.) “Well if you ask him real nice…”
or
b.) “I don’t know about that. He’s liable to turn around and bite you”
So this traveling salesman’s car breaks down on a lonely country road. He goes up to the nearest farmhouse, where an old farmer answers the door. “Well, you’re welcome to spend the night here, sonny, but there’s just one thing . . .”
There are multiple punchlines, offensive to all, but is it really a setup? I tend to think you need more, like “are skinnydipping”, “meet once a week to play poker”, “find a bag of money”, or (my personal favourite) “walk into a bar”.
The whole of the last one is: A priest, a minister, and a rabbi walk into a bar, and the bartender says “What is this, some kind of a joke?”.
Oh, yeah, point: can the OP provide some guidance as to at what point a setup becomes a setup?
Look at the genie joke I used as an example. In the joke that matches each punchline, the person who finds the genie is granted one wish. Unfortuantely for the person, the genie misunderstands the wish or grants it in a way not thought of by the wisher.