The guys had just wrapped up a formal news conference in Toronto -- when Bisping confronted GSP backstage and shouted at him for pushing him during the event.
GSP fired back, "F*ck off man ... I will break you."
At one point, Bisping faked like he was going to throw a punch -- GSP didn't even flinch.
They continued to cuss and threaten each other for a good 90 seconds before Bisping walked away.
But watch what happens at the very end of the video -- it's hilarious and heartbreaking at the same time.