If you mix the Ziegfeld Follies, Mardi Gras, the ball culture drag happenings of Harlem, the 1980s and a splash of Galliano—that is, the young couturier John Galliano—then add music and shake, what do you have? “Fashion Underground: The World of Susanne Bartsch,” the new show at the Museum at FIT. It’s a nocturnal world to be sure, with the Dionysian vibe of a midnight bacchanal. It’s also a more innocent world than the disco decadence that preceded it. For one thing, aside from the odd glass of bubbly, Ms. Bartsch keeps a clear head ...