Forget Paramount Network’s ill-advised TV update of Heathers: For a 21st century update on the “murderous high-school ennui” genre, you’re much better off with Thoroughbreds. Starring The Witch’s Anya Taylor-Joy and Bates Motel’s Olivia Cooke as disturbingly emotionless upper-class teenagers who plot to kill one girl’s stepfather after rekindling their childhood friendship, the film was a favorite of our own A.A. Dowd at last year’s Sundance Film Festival, where he called it a “razor-witted black comedy” that’s “superbly unpredictable, moving fluidly into thriller territory and back again.”