There weren't many scarier sights for players than an angry Sir Alex Ferguson.
Whenever Manchester United put in a sub-standard performance, the individuals most at fault certainly knew about it. Supporters lost count at the amount of times Fergie's half-time hairdryer treatment alone brought the side back from losing situations during his 26-year tenure.
It usually took a very brave man to stand up to the Scot and they wouldn't tend to stick around Old Trafford for much longer once Sir Alex judged them to be too big for their boots - see Roy Keane.
However, Fergie's fear factor wasn't enough to put off two Man United stars from mocking the boss with a classic dressing room prank back in the 2011/12 season.
Cristiano Ronaldo and Wayne Rooney became close friends during their time in Manchester together and it reflected on the pitch with the duo spearheading the attack of one of the best United teams in the last 15 years.
And Rio Ferdinand has revealed that their partnership extended beyond pitch when they once teamed up to cleverly engineer a way to make the manager look a bit silly.
As Ferdinand explains in the video for Copa 90 below, Ferguson was once issuing his pre-match instructions to the team before a Champions League tie against Benfica when Rooney casually rolled a ball in his direction.
The Man United boss went to kick it - only to be given a bit of a shock when Ronaldo, who had been hiding under a table behind him, grabbed Ferguson's leg as it swung back.
It understandably caused a few chuckles amongst the rest of the team and Fergie was confused at first: "What's going on lads?" he said.
Ferdinand went on to add that year's favourite for the Ballon d'Or, Ronaldo 'was always part of the team, in the camaraderie that went on in the training ground' during his time at Old Trafford.
The former Man United defender did not reveal whether Rooney and Ronaldo were punished for the prank but based on Fergie's reputation, you would assume he found a way to get back at the pair.