Father buys a lie detector that makes a loud beep whenever somebody tells a lie.
The son comes home in the afternoon. Father asks him, “So, you were at school today, right?”
Son: “Yeah.”
Detector: “Beep.“
Son: “OK, OK, I was at the movies.”
Detector: “Beep.”
Son: “Alright, I went for a beer with my friends.”
Father: “What?! At your age, I wouldn’t touch alcohol!“
Detector: “Beep.”
Mother laughs: “Ha! He really is your son!”
Detector: “Beep.”

THAT, is a good one!

I like, good one.