Oooops

A father buys a lie detector robot that slaps you when you lie.
He decides to test it out on his son at supper. "Where were you last*night?"
"I was at the library."
The robot slaps the son.
"OK I was at a friend's house," the son admits.
"Doing what?" asked the father.
"Watching a movie: Toy Story."
The robot slaps the son.
"OK it was porn!" cried the son.
Father yells "What? When I was your age I didn't know what porn was!"
The robot slaps the father.
The mother laughs and says, "He certainly is your son!"

The robot slaps the mother.