If you're not down with Joey Bada$$ you might get smacked the hell up ... like the photog outside Madison Square Garden who thought the rapper was A$AP Rocky.
Joey, part of the Pro Era crew, was feeling like a million bucks as he cruised out of Kanye West's show -- but watch what happened when one of the paps (not our guy) misidentified him.
All hell breaks loose until 2 cops on the scene step in between the guys.
NYPD says the photog filed a harassment complaint, but no one's been arrested or even cited.
Just to make sure this never happens to you ... take a good look.