I don't always listen to Katy Perry, but when I do its secretly Lee 'Scratch' Perry (and my neighbours are listening to it as well) Turn up the volume!
I almost always crank it if I'm playing still hard rock/metal era Def Leppard (aka pre-ADRENALIZE), Queen, Rob Zombie, or ACDC. Or if I have it on the local Classic Rock station. Or Pantera. I think it should be against the law to not crank it when playing them. Back on topic, Katy Perry has about as many hits that I liked as those that I didn't. And I am currently sick of Dark Horse, which has been played a lot around here lately.