Mariah Carey was in a bad mood Monday night, and she took it out on mortal enemy Jennifer Lopez.

We got Mariah leaving The Beverly Hilton hotel when she reaffirmed her dislike for J Lo, in the most high school of ways. She's said it before, and is not backing down.

As for why Mariah's mood was sour ... we're told the limo that was supposed to take her to the event honoring Brett Ratner bailed on her. Seems she was her typical late self, so she had to take a Lyft.

May the feud never die!