They became the most famous four words ever uttered by a tennis player but today, 30 years on, John McEnroe cannot remember exactly why he exploded out of control on Wimbledon's Court One. "You cannot be serious!" the then 22-year-old American had screamed at the umpire after complaining about a line call during his first-round victory over Tom Gullikson.
"I wish I could tell you that I remember," McEnroe said when asked if he recalled the line-calling being particularly bad in that match in June 1981. "It seemed like every match I played, from what I can recall, had some pretty bad line-calling. It was just one of those occasions where it all came together. I wouldn't say it was anything terrible. It wasn't the 15th bad call of the day."
If Hawk-Eye's all-seeing cameras have taken the sting out of modern-day arguments over line calls, it is also true that the characters at the top of the men's game are very different to those from what was another golden era 30 years ago.
Roger Federer and Rafael Nadal, the two great players of recent times, are eloquent champions who never have a bad word to say about one another and care deeply about the image of their sport. Bjorn Borg was as ice-cool as Federer is today, but the other major personalities of his era were made of more combustible material: Jimmy Connors, whose language and gestures could offend officials, opponents and public alike; Ivan Lendl, whose cold professionalism won him few friends; and Super Brat himself, who had already established a reputation as a loud-mouthed New Yorker in his four previous visits to the All England Club.
The behaviour of modern players may have improved, but, in Andy Murray, McEnroe sees a kindred spirit, a man who can find it hard to stop himself letting off steam. While McEnroe lambasted officials, Murray berates himself or shouts angrily in the general direction of his entourage.
"I've never seen him lose it as badly as I did, except at his coaches and the people he's yelling at in his box," McEnroe says. "That's where he goes off. I don't see it much with umpires. I see it all the time where he just spews nervous energy. You hope that the people he works with, or whoever he's directing that at, either have thick skin or are well-paid – or both."
The person who needed a thick skin back in June 1981 was Edward James, who clearly anticipated trouble in McEnroe's match against Gullikson. "I'm Scottish, so we're not going to have any problems, are we?" the umpire said to McEnroe before the match. McEnroe told James: "I'm Irish."
McEnroe won in straight sets, but the match will for ever be remembered for what happened after James gave McEnroe an official warning when the American smashed his racket following what he thought was a bad line call. The replacement racket was soon getting similar treatment after a serve was called long. "You cannot be serious!" McEnroe screamed. Following another disputed call, he directed perhaps the second most famous line in tennis history at James: "You guys are the absolute pits of the world!"
The umpire, who thought McEnroe had said "the piss of the world", deducted him a point for an obscenity. Pointing at James, McEnroe told Fred Hoyles, the referee: "This guy is an incompetent fool!"
After the match, McEnroe was fined $1,500 and threatened with an additional $10,000 penalty and expulsion if he misbehaved again. "It felt like there was so much pent-up nerves and expectation that I had put on myself," McEnroe recalled. "It had been built up as me against everyone there at the time, whether it was the press or the umpires. I remember thinking: 'If I win this tournament I don't want to come back.' When I did end up winning the tournament, though, I remember thinking within a few seconds: 'I want to come back and try to win this again'."
Having behaved for the rest of the tournament, which he finished by beating Borg in the final, McEnroe still found time to offend again. He declined the invitation to the traditional end-of-tournament dinner, pleading exhaustion, after which he became the first champion not to be offered honorary membership of the All England Club. He was admitted 12 months later, though in 1983 the club chairman, Buzzer Hadingham, still thought it necessary to write to ask him to behave or risk being thrown out of Wimbledon.
McEnroe, who jokes that the only occasions when he has subsequently repeated the "You cannot be serious!" line have been when he has been paid to do so, recalled the advice of his father, who was also his manager. "He always said: 'Look, if you're going to say something to an umpire, don't curse bluntly.' You're not going to get into trouble if you just say stuff like I was saying. I followed his lead for a while. I wish I had followed it longer."
Even John McEnroe Snr, who was usually calmness personified on court, would find himself the object of his son's tirades. McEnroe Jnr said: "I would get so worked up. I'd be yelling at him: 'I'm out here laying it on the line and you're sitting there?' I'd be all upset, yelling at him and in some cases, dare I say it, cursing at him. After the match he would say: 'John, did you say what I thought you said?' And I would say: 'No, there was someone up in the stands'."
McEnroe denied that it was gamesmanship. "I felt like I was hurting myself. So how could that be gamesmanship if you're out there self-destructing? You could make the argument that I was lucky that I wasn't defaulted.
"If you watch a guy go out on court and have a meltdown, you're not going to think: 'Oh my God, now I'm screwed.' Or you're not going to think: 'The umpire's going to give him calls because he's just told him he's an idiot or the pits of the world.' It's true that my opponents did sometimes have to wait, but is it unbelievably difficult to wait a minute instead of 20 seconds? I don't buy that argument."
McEnroe, who will again be part of the BBC commentary team at Wimbledon this year, recognises that it is easy to offer opinions from the sidelines, but he believes Murray hurts only himself when he launches into one of his outbursts. "I can tell you from experience that he is wasting a lot of energy which he should be saving for when he takes on guys like Rafa [Nadal] or Novak [Djokovic]," McEnroe says.
"It doesn't take someone like Einstein or Sigmund Freud to realise that it isn't helping him. I can tell you from experience that when you get that pent-up and crazed it can be distracting. It cost me the match in the French Open final when I lost to Lendl [in 1984, after McEnroe had won the first two sets]. I lost for no other reason than I got so wound up about how close I was coming to the win. It cost me the match and there will be an occasion where the same will happen to Murray. Maybe it already has."
Had McEnroe used tantrums as a way of motivating himself? "I think there would have been a better way of firing myself up without having to be on the edge of disaster. There are other ways to motivate yourself that I should probably have spent more time thinking about before I actually went out on the court. But it became a defence mechanism. If you're out there and things are going badly, are you going to cry or break down?
"I was always taught that you needed to be intense and never lose your focus. However, the first thing that came to my mind [in those situations] was often something funny. One of the things I respected about Connors was that one second he would be spewing a four-letter word, the next second he would do something that had people falling off the aisles. Yet he never seemed to lose his concentration.
"I would have loved to have been able to do that. I think the best part of commentating is that I'm able to show a side of my personality that was there that I wasn't able to get out on the court."