Ray J in Ray-Jing Fight After 'Fat Bitch' Insult

Ray J used another one of his appendages early this morning to take care of business ... this time beating down a dude in a violent confrontation that started when Mr. J called a woman a "fat bitch."

It went down at Club Nokia in downtown L.A. at 1 AM, after Mack 10 and Jamie Adler's West Coast Fest concert.

A woman goes nuclear on Ray J ... an eyewitness tells TMZ Ray J hurled the insult at her and she just goes off, screaming, "You said f**k me fat bitch." Ray J tries to calm her down, to no avail.

She has a couple of great lines ... "I'm the bitch they went to go get to whup bitches asses," and "I ain't no fake-ass n****r from Carson (Ray J's hometown)."

It's unclear how the fight started, but Ray J and some dude got at it, and it's pretty clear ... Ray beats the other guy's ass.

No one was arrested.