One day 7 year old Pete's grandma decides that Pete should go and stay with his parents for a while. She calls a taxi and tells Pete to get in. Then she goes round to the taxi driver and says:
"Listen, I'm giving you the money now. Just drop him off where I told you to. But be careful, he's a witty little squirt, so whatever he says, don't answer him."
The taxi driver says OK, and they go off.
After a few minutes, Pete gets bored. He leans forward towards the cab driver and says: "You know whaaat, if my mommy was a doctor and my daddy was a doctor, I'd be a doctor tooooooo." The driver doesn't even look.
Then Pete says: "You know whaaat, if my mommy was a teacher and my daddy was a teacher, I'd be a teacher toooooo." The cab driver silently clenchs his fists, but still holds himself.
But Pete says: "You know whaaat, if my mommy was a dentist and my daddy was a dentist, I'd be a dentist tooooo."
The driver, unable to hold himself, stops the cab, turns around and shouts: "Well you little bastard, what'd you be if your mommy was a bitch and your daddy was gay?"
"A taxi driver of course," replies little Pete.