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Piven was sidelined from "Speed the Plow" last December after suffering mercury poisoning from bad sushi.
Jeremy Piven still finds no humor in the sushi saga that sidelined him from his Broadway show last year.
The "Entourage" actor was backstage at Alexa Chung's MTV talk show last week when he began trading barbs with comic Chris Kattan over the toxic sushi that caused him to duck out early from his role in a Broadway show, according to the New York Daily News.
"So, what are you here to promote, your Broadway play?" Kattan reportedly asked Piven.
Piven left "Speed the Plow" last December after suffering mercury poisoning from bad sushi and is now legal battle with the show's producers who believe the actor made up the plan to get out of his contract.
The actor is apparently still hurting from the incident.
"Well, what are you here to promote? Mango?" Piven reportedly said referencing Kattan's "Saturday Night Live" stripper character.
The pair began to scream back and forth until Piven ripped into Kattan and said something "really personal" about the fellow comic's career, an insider told The News.
"He said, 'Whoa, man -- I thought we were just fooling around here,'" a source told the paper.
"I'm getting sued for that s--t!" Piven reportedly shouted. "It's not funny!"
Piven ran to the green room and slammed the door as nearly two dozen people listened to his profanity-laced tirade from outside, the source said.
"Chris felt really badly about the whole thing, so about 15 minutes later he tried to approach Jeremy again to apologize, to tell him he was just kidding and that he didn't mean to offend in any way," a snitch told The News.
"But Jeremy wasn't having it at all. He slammed the door in Chris' face again."
A rep for Piven denied the altercation took place, saying the two were just joking around before their appearances.
"Jeremy and Chris did see each other at MTV and they were joking around backstage before a talk show appearance, as many actors do," the publicist said. "If it was interpreted as a fight, someone wasn't paying attention."
Kattan's publicist said the two did square off and that the "Bollywood Hero" star tried to apologize to the fuming actor.
"Chris mistakenly asked Jeremy if he was there to promote his play and Piven fired back with 'What are you here to promote, Mango?'" Chris tried to apologize," the rep said.