A man with a tiny head walks into a bar

A man walks into a bar and orders a beer. The bartender notices the man's head is the size of a cue ball. "I've got to ask sir" says the bartender. "What happened?" The man says "my ship was sunk, a mermaid rescued me and promised me three wishes. For my first wish I asked to be returned to America. My second wish was to have a billion dollars. Finally, I asked to have sex with her, but she said mermaids can't have sex, so I asked for a little head!"