Sportswear tycoon Mike Ashley once hosted a management meeting in a pub where he drank 12 pints and vomited into a fireplace, a court has heard.
The Newcastle United owner is being sued by finance expert Jeffrey Blue at London's High Court.
He claims Mr Ashley often held meetings in pubs, and at one time promised to pay him £15m if he managed to increase Sports Direct's share price to £8.
He said the billionaire only paid him £1m. Mr Ashley disputes the claim.
Mr Justice Leggatt was told the dispute between Mr Blue and Mr Ashley related to an alleged conversation in a London pub called the Horse & Groom in 2013.
Jeffrey Chapman QC, who is leading Mr Blue's legal team, told the judge Mr Ashley's business practices flew in the face of "business orthodoxy".
Mr Blue said he had attended several senior management meetings at another pub, the Green Dragon in Alfreton, Derbyshire.
He said: "These meetings were like no other senior management meeting I had ever attended in all my years of investment banking experience."
Describing it as a "pub lock-in" where fish and chips and kebabs would be brought in after closing time, he said: "On one such evening, in front of his senior management team, Mr Ashley challenged a young Polish analyst in my team, Pawel Pawlowski, to a drinking competition.
"Mr Ashley and Pawel would drink pints of lager, with vodka 'chasers' between each pint, and the first to leave the bar area for whatever reason was declared the loser.
"After approximately 12 pints and chasers Pawel apologised profusely and had to excuse himself.
"Mr Ashley then vomited into the fireplace located in the centre of the bar, to huge applause from his senior management team."
Mr Blue said he first met Mr Ashley while working for Merrill Lynch in 2006.
"Mr Ashley was like no other client that anyone at Merrill Lynch had ever come across," he said.
"By way of example, his ability to express boredom and frustration during client meetings knew no limits, including various episodes where he would lie underneath meeting room tables to 'have a nap'."
David Cavender QC, who leads Mr Ashley's legal team, told the judge Mr Blue's claim was an "opportunistic try on".
The hearing continues.