Participants include everyone in a car, excluding the driver for safety purposes. When on the road, if people within the car see a car that has a headlight out, then that person yells sex and everyone participating hits the roof. The last person to hit the roof takes off a piece of clothing. Play ends when the car ride is over.
The informant claimed that this game is played for fun at night in cars, usually when the car is full or there are several people in the car.
I think this game probably came about as a way to make a boring car ride more interesting. It is common probably only with younger, teenage to twenties, crowds because of a sort of obsession and fascination this age group has with sex and nakedness. I would guess that there is a link between the acknowledgements of a headlight being out and the word sex being yelled, since headlight is often using as a metaphor for female breasts, hence the game involving a taking off of clothes.