Katy Perry, John Mayer Hit the Strip Club!

That's what you get for waking up in Vegas ... with John Mayer.

Katy Perry and her on-again, off-again maybe-boyfriend are not only hanging out again, they're doing so at strip clubs in Vegas. Good. Times.

They were spotted in Sin City early Sunday morning with a group of friends, having spent their night out at famed strip joint Spearmint Rhino.

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Katy and John recently began canoodling again after a brief split.

"They were together in a group," an onlooker said of the pair. "As for whether they got dances, they were in a strip club ... you do the math."

What math there is to do (beyond how many $12.50 Bud Lights one can rack up on a single tab) it's unclear, but they stayed out until 5 a.m.!

Earlier in the evening, Perry and Mayer checked into the Wynn Hotel - site of the now-infamous Prince Harry nude shenanigans - together.

What do you think? John Mayer and Katy Perry ...