A dad buys a lie detector robot which slaps people when they lie. He decides to test it at dinner.
"Son, where were you today?" The son says, "At school, dad." The robot slaps the son! "OK, I watched a DVD at my friend’s house"
"What DVD?" "Toy Story." The robot slaps the son again! "OK! It was porn" cries the son.
"What! When I was your age I didn’t know what porn was!" says the dad. The robot slaps the dad!
Mom laughs, "HaHaHa! He’s certainly your son." The robot slaps the mom.