ET to GO: Katy Perry Pinches Bieber's Butt?!

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In today's ET to GO: Katy Perry shuts down Hollywood Blvd. for the premiere of her new movie, and reveals that she may have pinched Justin Bieber's butt! And then Justin's steady, Selena Gomez, celebrates her "118th" birthday for her new movie Hotel Transylvania. But what is she doing for her real birthday?