The former manager has used his new autobiography to claim Keane, now a pundit, "thought he was Peter Pan" by the time the pair fell out spectacularly in 2005 and that his departure "was the best thing that could have happened" to United.
The book does not spare Wayne Rooney - "not the quickest learner" - or David Beckham, either, and confirms Ferguson was twice offered the England job as the recently retired Scot settles some old scores.
His animosity towards Keane has shown no sign of subsiding in the eight years since their row erupted.
Their relationship began to fracture as the midfielder became increasingly outspoken about his team-mates during a lengthy period on the sidelines due to injury and finally broke down when he gave an explosive interview to the club's TV channel.
The now infamous MUTV interview has never been aired on the channel but Ferguson claim that Edwin Van der Sar, Paul Scholes and Ruud van Nistelrooy were among the players who walked out when they were shown it privately.
The 71-year-old recalls Keane and Van Nistelrooy having to be pulled apart in a separate incident: "His [Keane's] eyes started to narrow, almost to wee black beads. It was frightening to watch, and I'm from Glasgow."
But after the MUTV interview, Ferguson says he could not get Keane out quickly enough. He told his assistant, Carlos Queiroz, at the time: "He needs to go, Carlos. 100 per cent. Get rid of him."
Ferguson, in his book, said: "In one deep sense, him leaving was the best thing that could have happened, because a lot of players were intimidated by him."
The Scot's ruthlessness as well as his man-management skills were a major factor in his success at Old Trafford and won him many admirers.
The Football Association have been among them and he claims they twice offered him the England manager's job - before Kevin Keegan was appointed in 1999 and again before Sven Goran Eriksson took charge in 2001.
However, Wayne Rooney will have a different opinion of Ferguson's managerial ability.
They fell out last season and the Scot has not made any easier for his successor, David Moyes, to repair the damage with the detail in his book.
Ferguson said Rooney is "not the quickest learner" and claims the striker, who had to be dropped after a drinking incident two years ago, was not fit enough to last a full game last season.
The book also repeats the former manager's assertion that the England international "wanted away" last term, which was a key factor in the player's unhappiness with the club.
Ferguson, outspoken as ever, says the way Rooney backed down after his 2010 contract also "made him look like a money man, and there was a residue of mistrust with the fans".
Beckham, who famously fell foul of Fergie in a spectacular dressing-room bust-up, was described as "the only player I managed who chose to be famous, who made it his mission to be known outside the game".
Ferguson insists he holds no grudge against Beckham but things were different when their relationship broke down in 2003.
In his new book, Ferguson said: "He was 12 feet from me. Between us on the floor lay a row of boots. David swore. I moved towards him and as I approached I kicked a boot.
"It hit him right about the eye. Of course he rose to have a go at me and the players stopped him. 'Sit down,' I said. 'You've let your team down. You can argue as much as you like'."
Two days later the story broke Beckham wore an Alice band in public to highlight his injury. Ferguson reacted decisively. "I told the board he had to go," he said.