The comedian skewered Hart during a portion of his stand-up set at The Wilbur Theatre in Boston Friday night, calling him a "midget with a regular ni**a's head" and a "punk bitch" ... among other insults.

Blackson also rips Kevin for essentially snitching on himself during his whole sex tape/extortion scandal.

Here's the backstory -- Blackson and Hart used to be friends, but Kevin took issue with Michael using his cheating fiasco as fodder for his comedy ... so he called him out during a 'Breakfast Club' interview by referring to Mike as "the Instagram model that just shows her ass and is looking for love."

Blackson took issue with that and vowed to keep blasting Hart, saying ... "when I'm done with you u will commit suicide by jumping off the curb you short f*ck."