Katy Perry Britney Spears Concert I'd Rather Watch Paint Dry

12/28/2013 7:05 AM PST BY TMZ STAFF
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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 ...