On November 18, 1992, Shannen Doherty delivered one of the most brutal lines in Beverly Hills, 90210 history. It happened in an otherwise preposterous season-three episode called “Wild Horses,” in which Luke Perry’s Dylan leaves town after being accused of cheating on the SAT and has an affair with an heiress while David Arquette guest stars as an abusive keytar player named Diesel. More important, Brenda (Doherty) and Kelly (Jennie Garth) are still feuding in the wake of Kelly’s hookup with Dylan...