Law enforcement and 'Kimmel' security sources tell TMZ ... the guy who's seen on video calling Jason a "p***y" is a regular at the studio and Hollywood premieres, and always shows up when celebs get their stars on the Hollywood Walk of Fame.

We're told the autograph-seeker gets famous people's signatures all the time ... and once in a while, he pops off like he did in our video after Jason's Thursday appearance on 'Kimmel.'

Our sources say celebs are just told to ignore the guy if he gives them crap about not signing ... but Jason relented and came over to sign autographs after initially blowing everyone off.

One source who has seen our video believes the autograph-seeker made a big stink to shame Jason into signing ... and it looks like it worked.

We're told there are rules in place for autograph hounds at 'Kimmel,' but the folks who come every day know the drill and know how to push the rules -- our sources say as long as no one gets physical, security at 'Kimmel' lets the autograph-seekers do their thing.

However, as one source tells us ... don't crap where you eat.

Thursday's exchange was pretty intense, but our sources say cops will not get involved in these situations unless Kimmel security calls them ... and we're told, for the most part, the autograph-seekers police their own when someone gets out of line.

Case in point, we're told cops weren't called over this incident.