Cruel Intentions (1999)

Two vicious step-siblings of an elite Manhattan prep school make a wager: to deflower the new headmaster's daughter before the start of term. Quenching a thirst for dangerous games, a promiscuous teen challenges her stepbrother to deflower their headmaster's daughter before summer ends. Sarah Michelle Gellar (I Know What You Did Last Summer, Scream 2, TV's Buffy The Vampire Slayer) and Ryan Phillippe (I Know What You Did Last Summer, 54) sizzle as a pair of unscrupulous siblings in a deliciously sexy tale of seduction, revenge and conquest. After cleverly seducing and ruining the reputation of an unsuspecting classmate (Selma Blair, Can't Hardly Wait, Zoe, Duncan, Jack & Jane), the sparks fly when Kathryn (Gellar) poses the ultimate challenge to her insatiable stepbrother Sebastian (Phillippe): deflower the Headmaster's beautiful, virgin daughter Annette (Reese Witherspoon, Pleasantville, The Man In The Moon). If he fails, Kathryn gets his most prized possession, but if he succeeds, Sebastian gets to possess and bed Kathryn. The stakes are high, but for Sebastian, the payoff is feverishly irresistible and before the summer's over, no one will escape their relentless game of cat and mouse until one of them is bitten by the most unlikely sensation of all...love.