'Superman' Villain Jack O'Halloran -- Christopher Reeve Was An Ass! I Nearly Knocked Him Out

One of Christopher Reeve's former co-stars is making outrageous accusations about his attitude on the set of "Superman" ... and this will blow your mind ... if you believe it.

We ran into Jack O'Halloran, who played Non ... the mute villain from Krypton ... and the photog asked him about working with Reeve -- and he ripped into the late actor for being a Prima donna who "believed his own publicity."

Now, up front -- we can't confirm any of O'Halloran's claims -- and to be honest ... we're really big fans of Christopher ... which is why this video was so shocking to us.

O'Halloran went on to tell a story about almost punching Reeve during a dispute on set and says, "He was like a child. He wanted to be Superman and Clark Kent all the time."

You gotta see his story about Reeve and the guy who played Jimmy Olsen too.

Again ... we're not necessarily buying 'em, but O'Halloran's stories are unique.