It's happens at about the 40-minute mark of almost every horror movie. The girl with the hottest body or the biggest boobs decides to take a shower for no apparent reason, has sex with a guy in the woods or she brushes her hair topless in the mirror. Less than ten minutes later she is killed by the villain because apparently they all hate it when girls get naked. Word to the wise, if you reach the 80-minute mark of a horror movie and the main girl hasn't gotten topless, it's not going to happen. Don't worry, if that happens you can probably find a nude picture of her somewhere online.
#10 Rhona Mitra In Hollow Man - Her Six Degrees Of Kevin Bacon include showing her awesome boobs.