In the monster movie 'Mosquito' a girl is in a tent when a giant mosquito flies in and bites her on the ass!
In 'Critters' a really nice looking girl gets shot in the butt by a slingshot.
Some real life incidents I have seen are:
On the X games a female downhill skateboarder fell of her board a high speed onto her backside and slid on the tarmac for a few meters, when she got up there was a big hole in her body suit over each of her buttocks and her ass was bright red and raw!