A boyfriend and girlfriend were driving down a deserted road surrounded by praries when the car ran out of gas.  

"Don't worry, I'll walk to the nearest gas station and get some," the boyfriend said.

When he'd gone his girlfriend got bored and switched on the car radio.   There was a local news report on about an escaped psycho who was armed and dangerous.   Then she heard a banging on the car roof.    It was annoying, so she turned some music on.    Then she found the car surrounded by police officers and heard someone shout:   "Come out with your hands up!"

She did, and saw the psycho she had heard about on the news report.   He'd been making the banging noise on the car roof - with her boyfriend's severed head.