Season 2, Episode 17: Carnal Knowledge

The twisted Blair plans a cruel revenge against her teacher, Rachel Carr, for her one bad grade, but has problems getting her posse of mean girls to rally for support since they are not keen to taking on a teacher. So, Blair starts a rumor that Miss Carr and Dan are romantically involved, which creates a firestorm of gossip, and she has her father, Harold, to back her up. But the final blows comes when Serena sees Dan and Rachel meeting at a local coffee shop and jumps to the wrong conclusion which Blair sees off her greatest victory, but also her most bittersweet one. Meanwhile, Chuck calls upon Nate and Vanessa for help when he wakes up in a strange hotel room and seek out a mysterious woman he met at a mysterious secret society party the night before which may had drastic consequences for him.