A man walks into a bar, and asks the bartender for a drink of water. The bartender pulls out a gun, points it at the man, and cocks it. The man pauses, before saying "Thank you" and leaving. What happened?

A man walks into a bar, and asks the bartender for a drink of water. The bartender pulls out a gun, points it at the man, and cocks it. The man pauses, before saying "Thank you" and leaving. What happened?