A man buys a a lie detector robot that slaps people who lie. He decides to try it out at dinner.
Dad: Son, where were you today during school?
Son: At school. -robot slaps son-
Son: Okay, I went to the movies.
Dad: Which one?
Son: Toy Story. -robot slaps son again-
Son: Okay, it was A Day with a Porn Star.
Dad: WHAT?! When I was your age I didn't even know what porn was! -robot slaps dad-
Mom: Ahahahaha!! After all he is your son! -robot slaps mom-