Fox News host Tucker Carlson loses his temper and yells obscenities at a historian in newly emerged footage being widely shared online.
The outspoken Donald Trump supporter was interviewing Rutger Bregman in the segment, which the controversial network later decided not to broadcast.
The Dutch historian became a viral hit after appearing at this year's Davos summit, where he called out billionaires, low tax rates and tax avoidance as being the world's greatest problems.
Carlson initially compliments Bregman on his Davos comments, but took offence at being called a "millionaire funded by billionaires".
"Why don't you go f**k yourself, you tiny brain," Carlson says in the video, which has now leaked online.
"I hope this gets picked up, because you're a moron. I tried to give you a hearing, but you were too f**king annoying."
Bregman had been saying that the desire for a higher tax rate on the world's richest people was mainstream - even by many Fox News-watching Republicans in the US - but said the issue was not given coverage as the wealthy elite suppressed it.
"We should really crack down on tax paradises and tax avoidance," Bregman told Carlson.
"In the 1950s and 1960s - the Golden Age of Capitalism, as historians call it - we had top marginal tax rate for the very rich of 70 to 90 percent, actually, under Eisenhower, the Republican president. This was one of the best periods in American history.
"The same is true for the UK and the rest of Europe... we should just go back to simple and straightforward solutions from the past."
Carlson appeared to start becoming annoyed as Bregman called out Trump for hiding his tax returns from the public, and suggested the Murdoch family (which owns Fox News) was "scapegoating immigrants" rather than "talking about the real issues".
After the interview was leaked, Carlson talked about it on his show. He admitted he was "rude" to Bregman, but defended his choice of language as "genuinely heartfelt".
"I called him a moron and then I modified that word with a vulgar Anglo-Saxon term that is also intelligible in Dutch," Carlson said.
"In my defense, I would say that that was entirely accurate but you're not allowed to use that word on television... It was genuinely heartfelt, I meant it with total sincerity."