50 Cent is ripping into Conor McGregor for calling him a bitch in Thursday's press conference ... mocking the UFC superstar for getting choked out by Nate Diaz.

ICYMI -- 50 called out Conor for using his famous "Floyd can't read" insult (which Fitty used when he was beefin' with Floyd a few years back) in Toronto ... saying T.B.E.'s "gonna kill him for saying that."

Conor responded to the NY rapper's comments during the Brooklyn stop of the world tour Thursday ... simply saying "50 Cent's a bitch!"

CONOR BEING CONOR
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Fitty didn't take it lightly, calling out the Notorious ... saying "What the f**k wrong wit this white boy, you fighting Floyd not me fool" ... and posting a pic of Conor getting choked out by Diaz.

Curtis added "champ about to be 50-0, and the Little leprechaun is just the 50th Victim. Floyd said 'I'm a put the hand of God on that boy.'"

Looks like Conor's gonna have to address this during the London stop of the world tour Friday ...

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