Trois lycéennes à Paris (1979)

Her parents throw a birthday party for her, but most of the guests are middle-aged, and she feels left out at her own party, until Marbeuf persuades her to join in the dancing, during which she displays an impressive cleavage while her mother looks on disapprovingly. Then there's a slow tune and the only young male guest at the party (Pjotr Stanislas) asks her to dance. During the dance they sneak into an alcove and have sex, hidden (but not very well) by some flimsy strands forming a curtain. Her mother discovers them in flagrante and Iris is thrown out of her home.