Well, this is pretty much as bad as a threesome in a car could go. (There's a video below, but it's NSFW-y.)
Firefighters in Wenzhou China had to rescue two naked women and a dude in his long johns when somebody bumped the parking brake in the middle of a threesome. The car rolled down a hill and into a tree.
The guy and one girl suffered minor injuries, but one girl ended up in the hospital with two broken legs.
Remember to scout your car sex locations carefully kids, and be sure you know what lever you're grabbing.
(Hat tip to Jesus!)