Cardi B Goes Nuclear on Nicki Minaj, Says She'll Beat Her Up

Cardi B and Nicki Minaj are at each other's throats again ... with Cardi threatening to beat the hell out of Nicki and pursue legal action.

Cardi was heated Monday as she ripped into Nicki during an expletive-filled tirade on social media, challenging her rival to a fight after Nicki went on her Queen Radio show and spilled more details about their infamous NYFW fight.

Cardi B called Nicki a snitch for claiming Rah Ali beat up Cardi during last month's brawl ... adding she's tired of the back and forth, so they should settle it with their fists.