A man walks into a bar and asks, “Got any grapes?”
The bartender, confused, tells the man no. The man thanks him and leaves.
The next day, the man returns and asks, “Got any grapes?”
Again, the bartender tells him, “No — the bar does not serve grapes, has never served grapes and, furthermore, will never serve grapes.” The man thanks him and leaves.
This goes on for almost a week, the man returns, but before he can say anything, the bartender yells, “Listen, man! This is a bar! We do not serve grapes! If you ask for grapes again, I will nail your hands to the bar!”
The man is silent for a moment, and then asks, “Got any nails?”
Confused, the bartender says no.
“Good!” says the man. “Got any grapes?”