Jason London Pleads Not Guilty in Bar Fight ... Sharting Allegations Linger

Jason London -- the guy who allegedly sharted himself in the back of a cop car after a bar fight in AZ -- has pled NOT GUILTY to disorderly conduct and assault ... TMZ has learned.

We broke the story ... London was arrested on Jan. 27 outside of a bar in Scottsdale, AZ ... after cops say he was a drunken mess ... who fought a bouncer and got violent with emergency responders.

According to police, the "Dazed and Confused" star intentionally sharted himself in the back of the cop car on the way to the police station ... and told cops, "I told you I'm happy as s**t."

Cops also say London berated them during the ride to the station .... saying things like, "Guess what fa**ot? I f**king love this. I f**king own you guys so hard."

But, Jason claims he was the real victim in the melee -- and was brutally assaulted by the bar's security staff for no reason at all. And then the next thing he remembers was getting arrested.

Following the incident Jason says he was left pretty beat up -- with an orbital fracture, sinus fracture, multiple contusions and a concussion -- and has since undergone multiple surgeries.