Looks like Russell Brand's bad-boy attitude might be rubbing off on his fiancee. Pop star Katy Perry served as a guest judge on this week's American Idol, and she certainly wasn't shy. While most guest judges tend to play it safe and shower the contestants with praise -- or at least sympathetically commend their efforts -- Perry showed her tough side. She even bickered with Kara DioGuardi over her choices and accused the veteran judge of being too lenient with her praise. With her straightforward style, could Perry be the perfect bad-cop replacement for Simon Cowell?