Justin Bieber's crew kicked the crap out of a guy in a nightclub parking lot ... leaving him bloody and bruised ... so claims the alleged victim who now plans to sue JB's saggy pants off.
As TMZ previously reported ... Bieber's crew is under investigation for the brawl outside a Southhampton nightclub last Sunday.
22-year-old Wayne Rennalls -- the alleged victim -- says he suffered facial lacerations and a possible broken tooth -- unclear why he says "possible."
As for how the brawl started ... Rennalls says it involves a bow tie and a girl -- he had loaned the tie to a waitress he had been talking to all night. He says he went to retrieve it and had the audacity to approach the woman while Justin was flirting with her.
According to cops, Bieber's people did go after the guy, but say he was aggressive toward them.
The police investigation is ongoing.