Lips (1981)

Kathy is not attracted to her husband John anymore, and Linda can't get horny for her husband Neil, who happens to work as a women's lingerie salesman. Psychologist Dr. William sends Linda and Neil to Dr. Jim Matlock, a sexologist who runs a quaint forest ranch that serves a safe place for impotent and frigid couples to spend their weekend hideaways and give in to any sexual desires they have. John and Kathy join them there as well as Stephen and Maria, another couple that's dealing with frigidity. Jim's gorgeous platinum blond neighbor Heidi seduces Neil. Jim spikes Stephen and Maria's drinks for a threesome. Meanwhile, in the nearby carpenter shop Skip, the owner, and his tomboy assistant Arlene have a fight after Skip once again hits on Arlene and she once again angrily refuses his advances. She leaves in anger, runs into Kathy and immediately seduces her. John, who went bird watching, catches them in the act which makes him so horny he starts giving himself a blow job. Linda sees this and helps out John. He eventually his way with Arlene to have his revenge on Kathy. In the process, Arlene discovers something about herself - that she's actually straight. Jim and his buxom assistant Cindy teach Kathy about sex.