Heathers (1988)

At Westerburg High where cliques rule, jocks dominate and all the popular girls are named Heather, it's going to take a Veronica and mysterious new kid to give teen angst a body count. Veronica, tired of the bullying and control by Heather Chandler, teams up with J.D, a dark rebel, to take revenge. They start by making Heather Chandler drink drain cleaner, making her die instantly. They cover up the murder and continue their killing spree by tricking Veronica into shooting two football players and making it look like a suicide. Veronica becomes scared of J.D and stops participating in his plans, causing him to plan to blow up the school. Veronica stops him by shooting him and becomes the new leader of the school.