This is, be warned, a Really Guilty one. But what’s the point of Guilty Pleasures if there’s no guilt involved? Listen, folks: one reason that a critic, like anybody else, goes to movies is to see beautiful people doing naughty things. In a word: sex! So flash back to the early 70s, when porn was briefly chic, and its makers fearlessly tested the bounds of legal behavior. Back then, hardcore had a naive vitality. It also produced a mini-masterpiece, School Girl, directed (pseudonymously) by San Francisco’s Paul Gerber and starring the sweetly enthusiastic Debra Allen as a college student researching a paper on local subcultures. She chooses the swinger scene, which leads to a half-dozen specialty numbers: boy-girl, girl-girl, group grope. In the most intriguing scene, a lithe young woman “directs” an erotic encounter with her husband and Debra. As firm and bossy as any auteur, the woman finally joins the deux to make a ménage à trois. It’s a funny, telling comment on how directors bring an audience’s gamiest desires to life, and on how power helps define any human relationship. But School Girl is also, ho-boy, sexy—or it wouldn’t be a guilty pleasure, would it?