It IS on – like Donkey Kong! Feud erupts between KATY PERRY and TAYLOR SWIFT in war of the words! JOHN MAYER to blame? 

No less than day  after Swifty said in a interview in Rolling Stone she has an enemy, Katy Perry took to Twitter to call out an unnamed mean girl.

“Watch out for the Regina George in sheep's clothing…” @katyperry Tweeted.

In the music mag Swift, 24, mentioned her new song “Bad Blood,” which she claims is about a female artist whom she’d had an uneasy relationship with, and whom, she claims double-crossed her.

“I was like, ‘Oh, we’re just straight-up enemies.’ And it wasn’t even about a guy!” Swift said. “It had to do with business. She basically tried to sabotage an entire arena tour. She tried to hire a bunch of people out from under me. And I’m surprisingly non-confrontational — you would not believe how much I hate conflict. So now I have to avoid her. It’s awkward, and I don’t like it.”

Swift admitted “I don’t think there would be any personal problem if she weren’t competitive.”

Both Swift and Perry, 29, have reportedly dated serial gal-pal-er John Mayer.

And yet, some of Swift’s dancers reportedly left her tour for Perry’s .

While Taylor may never ID the “Bad Blood” tune’s subject (she is rather fond of penning dittys about her ex BFs whom she dates for about 5 minutes), Perry’s tweet clearly ref’s Rachael McAdams’s character in “Mean Girls”.

Your move, Taylor.