A group of teenagers is gathered at a party. Music's playing; smuggled booze is flowing. Two girls grin sheepishly at each other as a crowd goads them on. Finally, the teens relent, rewarding their audience with some mouth-on-mouth action. It's not an unusual scene, according to South Florida high school students, who say the newest trend for teen girls isn't wearing the latest designer jeans or driving a cool car, but declaring themselves to be bisexual.