#4 Roy Keane vs Sir Alex Ferguson
Given both Sir Alex Ferguson and Roy Keane are renowned for their fiery temperaments, it's a wonder it took the two men so long to come to blows at Old Trafford.
That being said, when the two men did eventually clash, things escalated incredibly quickly.
After a rumoured fall-out over training facilities, Keane bashed several of his team-mates in an interview with MUTV that never aired but was shown to the team behind the scenes.
The interview caused a lot of backlash against Keane and he finally left the club, signing for boyhood club, Celtic, in 2006.
Both men have not shied away from taking swipes at each other in the years that have followed, with Ferguson running Keane down in his autobiography, and Keane being one of the first pundits to attack Ferguson and Manchester United during his subsequent media career.
Keane did, however, wish Ferguson well following his brain haemorrhage last year and that has been seen as a sign of goodwill between the two Manchester United legends.