As Mayweather’s Rolls-Royce was leaving the SSE Arena in London on Friday, dozens of McGregor fans swarmed Floyd’s ride … flipping him off and shouting insults at the car.

Security tried like hell to keep the hooligans away … literally ripping people from the car … but during the process, one guy appeared to get rocked by the front of the Rolls.

You can’t actually see the collision — but you can hear it — and you can see the security guy go flying down the street. He appears to be okay.

Eventually, Floyd made it out … but damn, craziness!!!