That didn't take long.

The claws were already off between Nicki Minaj and Mariah Carey on the season premiere of "American Idol" last night ... and one of the fights was over "Mean Girls." How fitting, right?

The two got into it right away, during the first audition.

After a contestant called Mariah's "All I Want for Christmas Is You" the best holiday song ever, Mimi couldn't help but brag ... prompting Nicki to say "She's a bitch, she's a bitch, she's a bitch!"

Check out Carey's diva reaction in the video above.

That wasn't the end of it though -- the two then got into a weird battle about who knew the characters of "Mean Girls" better. Seriously.

Who do you think is the Regina George in this situation? Nicki or Mariah ... or both of them? Sound off below!

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