Because that's what other parents would say, actually. Some months ago I came out of our house and saw an approximately 12 year old boy working on my bike with a wrench. He apparently wanted to steal the pedals. After I told him to get lost he called me a dumb cunt, which earned him a firm slap.
Ten minutes later he came back, with his fuckhead of a father in tow, who threatened me that he'd go to the police. The notion that his fucked up offspring wasn't only a thieve but also had no manners whatsoever never crossed the father's head.
Also, the youngster was too dumb to realize that pedals have a left-hand thread, at least one of each pair.