Dad buys a lie detector robot which slaps people when they lie.
He decides to test it out on his son.
“Son, where were you today?”
The son says, “Watched a DVD at my friend’s house!”
The robot slaps the son!
“Ok, it was a porno” cries the son
“What! When I was your age I didn’t know what porn was” says the dad
The robot slaps the dad!
The mom laughs, “He’s certainly your son!”
The robot slaps the mom!