TMZ is reporting that "Idol" auditions in Charlotte, North Carolina were "derailed" yesterday, when Nicki CURSED at Mariah . . . and THREATENED her by shouting, quote, "I'm gonna knock you out!"

It's hard to hear what Nicki is running her mouth about . . . but TMZ did provide a transcript.  Here's what they say she said:

"Get this [crap] in self control.  Get in control.  Don't lose your head . . . Don't tell me I'm a gangster . . . So every time you patronize me, I'm-ma take it back, and if you've got a problem, handle it . . .

"I told them I'm not  putting up with her  highness over there.  Figure it out . . . I'm not gonna sit here every minute to have you come down and harass me every minute everyday."

Mariah is talking back at Nicki but it's hard to hear what she's saying.

Supposedly, the producers even shut down filming for the day so the judges could "cool down."  And there's word that the show IS starting to worry about them being able to coexist throughout the season.