John Waters is a niche, independent filmmaker and you may go your whole life without having seen one of his films. But if you see one, see “Hairspray.” This 1988 musical about integration told through a Baltimore teen dance TV show is more commercial than his other fare, but that’s not why. You should see it because it shows Waters at the height of his writing/directing powers and it offers a lesson in how much campiness is the perfect amount of campiness for a campy film to be a good film. It’s also fortified with the right amount of irony.