In a teaser video called “World’s Worst Birthday Party Entertainers,” Katy Perry does her best bar mitzvah DJ: “Yosef Shulem,” a curly haired, yarmulke-wearing fast-talker who sounds an awful lot like Katy Perry. Offensive? Not really. Is she maybe ruining her new single’s chance at Song of Summer stardom with all this? No way; “Birthday” is a smash. She also does an apathetic clown, a hillbilly animal trainer, and a Twitter-loving princess if you’re looking to book your your next party.