The first rule of being Mariah Carey: don't come for the Queen Diva unless she comes for you.

On Sunday's episode of Bravo's "Watch What Happens Live" with Andy Cohen, The Elusive Chanteuse was the queen of polite deflection when it came to her alleged $50 million breakup and rumored new boo. But when it came to Demi Lovato and her public disapproval of Carey's shady ways, Mariah didn't pull ANY punches.

The root of this feud is from an early-2000s interview, in which Mariah was asked what she thinks about Jennifer Lopez, and Mariah responds...

photo: Giphy

Mariah later clarified that this comment isn't as bitchy as it may first appear — she was trying to say that she doesn't know J.Lo THAT WELL. “I’m not gonna put on a thing like ‘We’re all Hollywood and let’s just all pretend we’re best friends because we’re in that land,'" she said. "It wasn’t like I don’t know who she is. Of course I do. That wasn’t the question.”

However, that wasn't enough to get people to move on — including Demi Lovato.

Even though this shade happened almost 20 years ago, Demi Lovato has been PUBLICLY dragging Mariah for her "rude" remarks.

Lovato shaded Carey with a comment on a nasty meme, implying that Mariah is nothing more than a washed-up Ariana Grande.

"Wrong way around, honey."

BURN.

“Mariah is a legend and is so talented but constantly disses people," Lovato wrote after Carey's fans came for her. "It’s nasty the way she treats Jennifer.”

When Cohen brought up Lovato, Mariah was OVER IT before it even began.

When asked what she would say to Lovato, Carey responded with the clap back heard around the world by saying "I don’t know her either."

Yikes!

“I wouldn’t say anything to her," Mariah added.

"She should come up, introduce herself to me, say ‘here’s my opinion, what do you think about it?’ That’s how you handle shit, OK.”

And if Lovato or anyone else is wondering, Carey confirmed on the show that she still doesn't "know" J.Lo and isn't even familiar with Ariana Grande.

"Honestly I'm not familiar. I listen to hip hop more than I listen to pop music," she said during a game of "Does! She! Know Her!?"

You can watch the shade that could protect from the fire of a thousand suns below.