Justin Bieber: Today's Lesson ... Don't Call a 6'5" Fan a Motherf*****

8:20 AM PT -- Lamont now says he's NOT the guy who fought Bieber ... even though he totally owned it on Thursday. He says he's been getting death threats from Beliebers and even got fired from his job.

Remember, he posted a video on Thursday talking about the fight. He's now saying he lied, though it's unclear WHY he did so.

Justin Bieber incited the 6'5" man who brawled with the singer by calling him a motherf***** ... this according to the very large guy himself.

Lamont Richmond is the guy with whom Biebs picked the fight. We're told this is how Lamont's story goes ... he'd just left a bar when he saw Justin outside the Westin in Cleveland. Lamont says he and his 2 chick friends chilled with Bieber for a short time.

Check out the photo below. Lamont says he dared to ask Bieber if the women could take a pic and get a John Hancock. Lamont says Bieber snapped back, "No autographs tonight, motherf*****."

Lamont says Justin reeked of alcohol and got all Quien Es Mas Macho on him, "puffing his chest up," and then took a swing. That was enough for Lamont.

You see Lamont restrain Bieber in the video ... and says he's sure, if he went full force, he would have killed him.

We're told Lamont has already met with a lawyer and plans to sue. For what is anyone's guess.