Tommy Fury has warned that Jake Paul would not last 30 seconds in a boxing ring with him.
The younger brother of Tyson Fury and the YouTuber-turned-boxer's ongoing row turned up a notch on Wednesday night.
Paul's impersonation of Fury, faking an English accent and removing his shirt, drew an irate response.
Fury said, while wearing fake hair to mock Paul's look: "I don't know how you take yourself seriously.
"I put it on a plate for you, I asked if you wanted to fight, and you decided to laugh it off as per usual.
"Stick to your little YouTube, behind your little desk, and don't come over to this boxing world because you will get laid out in 30 seconds flat!"
The rivalry began 24 hours earlier when WBC heavyweight champion Tyson Fury posted on social media in praise of his younger brother and suggested a fight against Paul.
Paul replied: "You are Fury's little brother? If you want to do something don't let your brother do it for you."
Tommy Fury hit back: "Mr Jake Paul, I don't need anybody to do my dirty work. I'll call you out right now myself.
"You can fight me any time, any place, anywhere. All you've got to do is get in touch."
Tommy Fury, who found fame on Love Island, has impressively won his first five fights and is an emerging light-heavyweight prospect.
Paul has won both of his pro boxing matches, against fellow YouTuber AnEsonGib and basketball player Nate Robinson.
He will face former UFC fighter Ben Askren, who has posted footage of his boxing training online, on April 17.
Paul also took to criticising Saul 'Canelo' Alvarez, the Mexican phenom who beat Avni Yilidirim last weekend to set up a unification fight with Billy Joe Saunders.
Canelo appeared to throw Paul fans out of the ring after his fight, prompting the YouTuber to call him a "hater" and demand he fights Jermell Charlo, Caleb Plant, David Benavidez, Demetrius Andrade or the retired legend Andre Ward.