Lip Service (1974)

Sidney Spelvin, a sexually frustrated fireman, complains to Dr. Cousins, a female psychiatrist, that his wife will only have sex in the missionary position. That doesn’t please Sidney because he’s learned (from various gurus) about 197 other ways to bring a woman to orgasm. Interested in those 197 other ways, Dr. Cousins quickly cajoles Sidney into demonstrating those techniques on her, for "clinical purposes" only, right there in her office. Oh, those wacky porno shrinks!