Canadian pop-punk, passive-aggressive Twitter feuds are a riot, eh? It's been three years since Avril Lavigne ripped ex-husband Deryck Whibley's heart out of his chest and filed for divorce, citing "irreconcilable differences" after three years of marriage. Lavigne's now engaged to Chad Kroeger, becoming heir apparent to Nickelback's mountain of Canadian cash. And Whibley's moved on too; he's dating model Ari Cooper. But Lavigne's happiness is Whibley's punch line. The Sum 41 frontman and his girlfriend recently dressed up like Avril and Chad, respectively, for a Halloween party, posting a picture of their cross-dressing costumes on Twitter. "Hey Deryck, loved the costumes!" Kroeger tweeted in response to the photo. "We were going to dress up as you guys this year but all the parties had celebrity themes haha." Haha? The joke's on Chad; the music at his next wedding's going to be made up primarily of Avril Lavigne tunes and Nickelback ballads. There's nothing rock 'n' roll about that. Sum 41, however, they're still pop-punk as shit.