Paulie Malignaggi just "bitch slapped" and promised to kill Conor McGregor's good friend Artem Lobov ... and the guys he 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 .