Sir Alex Ferguson wasn't one to shy away from confrontation.
But even the fiery Scot decided enough was enough when Ruud van Nistelrooy swore at him in the Manchester United dugout, during the 2006 Carling Cup final.
Ferguson had named the Dutchman on his bench in Cardiff with Wayne Rooney and Louis Saha starting up top for the Red Devils.
United won the match 4-0 and everyone involved with the club was obviously delighted.
But down on the touchline the atmosphere wasn't one of initial celebration, as Van Nistelrooy vented his fury at not being brought on.
According to Ferguson, who explained in his book, Van Nistelrooy even ended up swearing at the Scot, prompting United assistant Carlos Queiroz to wade in.
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Queiroz confronted Van Nistelrooy after the insult as things threatened to turn ugly.
Ferguson described the incident as "fractious", adding it was ultimately "the end" for the former Holland international.
That summer Van Nistelrooy was sold to Real Madrid, where he spent four seasons with the La Liga giants before signing for Hamburg and finally Malaga.
Van Nistelrooy ignored the incident in the years following, but in 2010 made a phone call out of the blue to Ferguson.
"I had been thinking about it for a while and talking it through with my wife," Van Nistelrooy later explained.
"Two or three times every year I would think to myself what a shame it was that it had ended like it did with Ferguson. I wanted to do something about it.
"My wife suggested I send Ferguson a text to see if he was willing to talk and when I sent him a message asking if I could ring him he replied to say: 'OK, call me at this date and time.'
"I rang him and he answered and said: 'OK, fine, go ahead.' I said I wanted to apologise for what had happened and he replied: 'Fine, I appreciate that, when we meet again it will be OK.' That was great to know."
Has Sir Alex Ferguson right to sell Ruud van Nistelrooy? Have your say here.
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