Nicki Minaj SLAMS Mariah Carey -- You're a Bitter Old Woman!

In case you forgot ... Nicki Minaj STILL HATES Mariah Carey ... and moments ago, she went after the diva AGAIN ... calling her a bitter old woman with no personality.

Minaj just unloaded on Twitter, following a series of heated exchanges on "American Idol" last night. During the show, Mariah spit a little trash talk Nicki's way ... and taunted her for never having a #1 single on the Billboard Hot 100.

Nicki took some shots back at Mariah on the show -- at one point breaking out a cotton swab and telling Mariah to clean out her ears.

But moments ago, Nicki continued the war on Twitter ... telling critics to ask themselves "Why a woman SO successful at her age, is still so INSECURE, and bitter."

Minaj also made a reference to reports that "Idol" producers were recently looking to replace Mariah with former judge Jennifer Lopez:

"All dem #1s but JLo phone ringin? Lol. I guess having a personality, being a secure woman, and giving genuine critique still trumps that." So far, no response from Mariah.

Of course, Nicki and Mariah have been at each other's throats since before the season even began ... 'memba this video from last year?