One of the classic sleeping/driving pranks is waiting for your passenger to fall asleep, then tapping the brakes and screaming. It never fails to jolt them awake in a fit of terror and lets them know you're an asshole of a friend who shows no mercy.
This man took that prank, added some slasher movie tactic, and scared (probably literally) the shit out of this sleeping friend.
I really hope he enjoyed that, because his car upholstery probably smells like piss now.
Granted, Homer Simpson did do it first. But still -- TERRIFYING.