Tyson Fury goaded Wladimir Klitschko by taking off his top and telling the Ukrainian he lost his heavyweight titles to "a fat man".
Fury claimed the IBF, WBA, WBO and IBO belts by defeating Klitschko in November, but has since been stripped of the IBF title, which fellow Briton Anthony Joshua now holds.
Klitschko will get a shot at revenge against Fury in Manchester on July 9 and the latter did his best to embarrass his opponent.
The 27-year-old removed his shirt during a media conference and claimed Klitschko should be ashamed of losing to an opponent in such condition, saying: "Does that look like a fighter's body? Clearly not. That's who beat you. Shame on you. A fat man beat him and relieved him of all his belts.
"I don't take boxing seriously, as you can tell. It's about getting a few quid and putting food on the table. What's the point in practicing your job for 40 years if you can't beat a fat man?"
Fury insisted he has no interest in the sport and only takes part because of the money on offer.
"Boxing doesn't even mean much to me otherwise I wouldn't go into camp four stone [heavy] every week having eaten every pie in Lancashire and drunk every pint in the UK," said Fury.
"I hate every second of training. I hate boxing. I hate the lot. I hate speaking to you idiots [the media]. I'd rather be at home watching television with my kids and eating chocolate. I hate boxing, but I'm just too good at it and I'm making too much money.
"People do these sports for different reasons. Wladimir is already a multi-millionnaire so it's obviously something he loves to do. When you're like that, you're capable of anything.
"I don't live a strict lifestyle. I don't live an athlete's lifestyle. You couldn't call me an athlete."