A man buys a lie detector robot that slaps people who lie. He decides to test it at dinner.
DAD: Son, where were you today during school hours?
SON: At school.
The robot slaps the son.
SON: Okay, I went to the movies.
DAD: Which one?
SON: MIB 3
The 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.
The robot slaps Dad.
MOM: Ha! That's what you get. After all, he's your son.
The robot slaps mom.