It happens every weekend: In a haze of hormones and alcohol, groups of male and female college students meet at a frat party, a bar, or hanging out in a dorm room, and then hook up for an evening of sex first, questions later. As casually as the sexual encounter begins, so it often ends with no strings attached; after all, it was "just a hook up." While a hook up might mean anything from kissing to oral sex to going all the way, the lack of commitment is paramount.