Cruel Intentions (1999)

Kathryn Merteuil and Sebastian Valmont are seductive, manipulative step-siblings who get what they want when they want it. Kathryn makes a bet with Sebastian: Sebastian must bed Annette, daughter of the headmaster at their school, before the end of summer break. Annette has stated that she would wait until love and marriage to sleep with a man. If Kathryn wins, she gets Sebastian's vintage 1959 Jaguar Roadster. If Sebastian wins, he gets Kathryn, the only girl he knows he'll never have. Also in play is Cecile, a naïve girl whose mother had enlisted Kathryn to help her fit in at her new school. However, Kathryn (with Sebastian's help) plans to ruin Cecile's reputation as revenge on Kat's ex-boyfriend, who left her for Cecile.