As part of our 'A Point in Time' series, Wimbledon.com takes a closer look at some of the best - and most significant - points in the history of The Championships. This week, it's one of the most famous - or infamous - line calls ever heard during the Fortnight...

Essentially, this was an argument about, of all things, chalk. To be more precise, as this was all about precision and accuracy and getting things right, it was a dispute about the tiniest puff of titanium white dust. 

From where John McEnroe was standing - admittedly, on the other side of the net - he was sure he had seen a "spray of chalk" from his serve hitting the back of the line. The umpire, Edward James, didn't disagree, though that didn't mean he would be over-ruling the linesman's 'out' call. "There was chalk," James said, according to McEnroe's account of what happened during his opening match at the 1981 Championships, "but it was chalk that had spread beyond the line."

For McEnroe, this was about more than just the chalk. When the ball left his racket, he had 'felt' that the serve was a good one. 'Feeling' whether a shot was in or out, now that wasn't an option available to the umpire or his linesman, and McEnroe was sure he was right. The scene was set for McEnroe's masterpiece. 

The first round of Wimbledon always made McEnroe tense and agitated, but this time the stress and angst was horrific: "The devils were crawling all over my brain that afternoon." 

A pre-match conversation with James hadn't helped. "The umpire, a pleasant enough middle-aged gentleman, came up to me when I first walked on to the court and said something that seemed totally off the wall

"'I'm Scottish so we're not going to have any problems are we?' I guess since my surname started with 'Mc' he thought we were soul brothers. 'I'm Irish,' I told him, curtly. Nervously. Things went downhill from there," he would later recall in his memoirs. 

This wasn't the first time that McEnroe, the runner-up to Bjorn Borg the previous summer, had misbehaved at the All England Club. And it's not as if London hadn't been warned as just days before at the Queen's Club tournament he had shouted out: "I'm so disgusting, you shouldn't watch - everyone leave." But never before had he provided such theatre. "Chalk came up all over the place. Man, you can't be serious," he said, before going on to say the most quoted line in tennis history: "You cannot be serious." He went on: "That ball was on the line. Chalk flew up. It was clearly in. How can you possibly call that out? Everyone in the stadium knows it's in and you call it out?"

That wasn't the only memorable line of the afternoon as, after another squabble over a line-call, McEnroe told James: "You guys are the absolute pits of the world." James, who thought that McEnroe has called him "the absolute piss of the world", punished the New Yorker: "I'm going to award a point against you because you're rude." But clearly that wasn't the line that everyone will remember from McEnroe's straight-sets victory. Within a fortnight, McEnroe would be the Wimbledon champion for the first time. But what still has everyone talking? That first Wimbledon title? Or those four words, "you cannot be serious"? 

'THE SHAME OF JOHN MCENROE,' said the headline in one London newspaper, while another declared: 'DISGRACE OF SUPER BRAT.' 

Full of rage and then full of remorse, McEnroe put it best himself, in his autobiography titled, 'You Cannot be Serious': "It was a scream that came straight from Queens [in his native New York, and not the tennis club in west London], but that has travelled very far in the years since."