Anthony Joshua promised to knock Jarrell Miller out as the pair clashed at a heated news conference at Madison Square Garden on Tuesday.
WBA, WBO, IBO and IBF heavyweight champion Joshua will make his United States debut against Miller in New York City on June 1 and sparks were flying from the off at a media event.
Miller shoved Joshua hard in the chest within seconds of taking to the stage, before security intervened on multiple occasions as promoter Eddie Hearn ushered the British fighter away.
The confrontation prompted a change of format for the news conference, with Hearn encouraging the two athletes to stay in their seats rather than approach the podium.
"I'll sit down when I feel like it," Miller responded. "I'm home," he then shouted, banging the desk in front of him. "[Joshua] is not from these streets, and he's going to come here and tell me I'm the underdog?"
Hearn described the start of the event as "a little bit spicy" and the heat rose again as the pair took the microphones.
Miller said: "I'm ready. You have no idea. I breathe, eat, sleep Anthony Joshua.
"I've got a picture of him as my screensaver. Anthony Joshua. I've got a picture on my wall. Anthony Joshua. I wake up in the morning and think: Anthony Joshua."
The American then repeatedly interrupted Joshua as the two traded jokes and insults, leading the Briton to ask: "How old are you?"
He added: "Miller's a little b****. I'm going to knock him the f*** out on June 1. There's no doubt about that."
Joshua extended the event even after Miller departed the stage, telling reporters of the deal behind the fight: "I just gave him a big pay check, some cheeseburgers, and he was ready, he was there.
"He has no brain, so it's not hard to get inside his head. It was an easy negotiation."