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."
*robot slaps son*

"OK, I was at a friend’s house."
"Doing what?" asked the father. Son: "Watching a movie. Toy Story."
*robot slaps son*

"OK, it was porn!" cried the son. Father yells, "What!? When I was your age I didn't know what porn was."
*robot slaps the father*

The mother laughs and says, "He certainly is your son."
*robot slaps the mother*