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Britney Spears blew everyone away during her Vegas debut last night ... everyone, but Katy Perry.
Katy was front and center for the "Piece of Me" show -- rubbing elbows with Miley Cyrus and Adam Lambert -- and while Miley danced her ass off, Katy couldn't seem less interested.
True enough ... Britney's no John Mayer, but come on Katy -- she's a much better dancer than him.
As they say ... you can please some of the people all of the time ...
