Fueled by an ad for Gap khakis and some airtime on MTV, swing dancing is the latest fad to hit college campuses. At Stanford, 100 students tried out for 20 openings with the Stanford Vintage Dance Ensemble. (More than a thousand others enrolled in social dance classes winter quarter; many lined up overnight to guarantee their places.) In January, seniors Theo Alkousakis and Deb Henigson did the lindy hop in a performance at Roble Gym.