tried it once, didnt like it

A man walked into a bar on a slow night and sat down. After a few minutes, the bartender asked him if he wanted a drink.
He replied, "No thanks. I don't drink. I tried it once but I didn't like it."
So the bartender said, "Well, would you like a cigarette?"
But the man said, "No thanks. I don't smoke. I tried it once but I didn't like it."
The bartender asked him if he'd like to play a game of pool, and again the man said, "No thanks. I don't like pool. I tried it once but I didn't like it.
As a matter of fact, I wouldn't be here at all, but I'm waiting for my son."

The bartender said, "I'm guessing he's an only child."