Laughter is the best medicine

A man buys a lie detector robot that slaps people who lie. He decides to test it at dinner.
Dad: Son, where were u today during school hours?
Son: At school *Robot slaps Son*
Son: Ok i went to the movies
DAD: Which one?
Son: ToyStory *he slaps son again*
son: Ok, it was day with a porn-star
Dad: what! When i was your age i didn't even know what porn was! *he slaps dad*
Mom: HAHA! After all he's ur son *he slaps mom*