Paulie Malignaggi just "bitch slapped" and promised to kill Conor McGregor's good friend, Artem Lobov ... and the guys ain't even scheduled to fight yet.
Malignaggi -- a former world champion boxer in 2 weight classes -- was at a promotional event for Lobov ... a former UFC fighter who's fighting in the Bare Knuckle FC this weekend.
Paulie recently signed with BKFC as well ... and he wasted no time making his presence known.
The 2 fighters came face-to-face at Mendez Boxing Gym in NYC on Tuesday ... where Malignaggi smacked the hell outta Artem, before yelling, "that was a bitch slap for a bitch" ... and telling Artem, "I'm going to put you in a body bag."
This ain't random beef ... Lobov is one of Conor's best friends -- and McGregor and Paulie have major issues.
Remember, Paulie was one of Conor's training partners as he prepared for the Mayweather fight ... but the relationship went to hell after footage of The Notorious getting the best of the former boxing champ was published.
Lobov clapped back on Instagram ... saying, "I am told you got a sly cheap shot in, I thought that was a mosquito!"
"You know you get killed in a minute if the people werent there, You will be paying with your broken jaw!"
With all this heat surrounding the matchup ... seems there's no way the Bare Knuckle people are gonna miss out on the opportunity to make this fight.