#3 Jose Mourinho and Pep Guardiola
Jose Mourinho and Pep Guardiola used to be ‘friendly’ back in the late 1990s at Barcelona but their circumstances since then have soured the relationship between two of the most successful managers of modern football. First, Guardiola was appointed the manager of Barcelona ahead of Mourinho, then it was the Champions League final between the Blaugrana and Inter Milan in 2010, their rivalry intensified as managers of Barcelona and Real Madrid and now, of course, they are in charge of the two Manchester clubs in England.
Their relationship extended far beyond managerial rivalry years ago and there seems to be nothing but a festering pool of hatred left. Both men have criticised each other's tactics repeatedly, one focused on playing pragmatic need-based football and the other insisting on playing a beautiful game.
In a famous rant after their UCL semi-final clash in 2011, Mourinho said, "One day, I would like Josep Guardiola to win this competition properly... I would be ashamed to have won it with the scandal of Stamford Bridge. If he wins it this year, it will be with the scandal of the Bernabeu... I hope one day Guardiola has the chance of winning a brilliant, clean championship with no scandal."
By the next season, the two were at it again as the Spanish Super Cup at the start of the 2011-12 season broke out into an all-out brawl where Mourinho even poked the late Tito Villanova in the eye. While hostilities have not quite escalated in Manchester in a similar fashion, there is no love lost between these two greats.