A duck walks into a bar and asks: "Got any grapes?"

A duck walks into a bar and asks: "Got any grapes?"
The bartender says no, so the duck leaves.
The next day the duck walks into the bar again and asks: "Got any grapes?"
The bartender says no again, and adds: "This is a bar.", so the duck leaves.
The next day the duck walks into the bar, but the bartender cuts him off by telling him: "We do not serve grapes here, and if you ask for grapes one more time I will nail your beak to the bar!"
The duck asks: "Got any nails?"
The bartender says no, and the duck replies: "Good, got any grapes?"

This joke is the first "An X walks into a bar..." jokes that I am looking at. Perhaps I will do a whole series of them. The critical element of the joke is the fact that the bartender threatens to nail the duck's beak to the bar, but since he has no nails, the duck assumes that the threat was hollow and precedes to ask about grapes.

Not only is the duck intelligent enough to notice that the bartender will not follow through on his threat, but also he is a jerk about it.

Another humorous part of the joke is the repetitive nature of it. The duck just keeps asking for grapes. It is sort of unexpected each time it occurs, so it become funnier as it goes on.