Rent Class (1983)

When wealthy pre-school senior Skip (Rob Lowe) learns that his shy new roommate Jonathan (Andrew McCarthy) is a total loser at romance, he sends the aspiring young Romero to the city to learn the ropes - before he ruins both their reputations. But when Jonathan is seduced by a sexy older woman named Ellen (Jacqueline Bisset), he begins a zany, romantic mis-education that stars with a double major in lust and deception - and ends with the uproarious discovery that not only is Ellen the woman of his dreams…she's also Skip's mom!