Here is a one Harrison diatribe to a chair umpire last year, as quoted in the New Yorker: "That's terrible. The ball wasn't out. You've missed, like, 17 calls in two days. I mean, you've missed so many! That's awful! You're sitting here on a chair and you can't see that. That's unbelievable! Come on, man, you have to pay attention! You have to pay attention! You shouldn't be sitting in a chair if you're not paying attention."
Harrison admits it is an ongoing battle to channel his fierce desire and will to win into a positive force: "I am a very competitive person and I fight for every point but sometimes I show my frustration on court a little too much," Harrison told the Herald on Sunday. "I am working on it though."
He added that one of his goals for 2012 is to be "a little bit more composed and under control with things to maximise my potential for this year".
Certainly the occasional outburst will be tolerated, much as it was with McEnroe and still is with Roddick, if he continues on the trajectory of the past few years.
In 2008, he became just the 11th player in ATP history (and the first since Rafa Nadal in 2002) to win an ATP match before his 16th birthday, beating Pablo Cuevas (then world No95) in Houston. At the time, the 15-year-old Harrison carried a world ranking of 1288.
He progressed steadily up the tree from there, despite the constant focus from hopeful stateside media looking for a new champion. Across the 1990s, American men won 21 of the 40 grand slams; no other country took more than three in the same period.
The 2000s were vastly different, with just four majors, the last by Roddick back in 2003.
There have been many 'next big things' since then - think of James Blake, John Isner, Sam Querrey and Donald Young - and Harrison is the latest.
"I think there is just a lot more competition in the world today and players are developing from a number of different countries," says Harrison.
"American tennis was blessed to have so many great players like Sampras, Agassi, Courier and Chang but I also think Roddick, [Mardy Fish] and the other guys are doing pretty well. It is a privilege to be considered a hope for my country. To be mentioned in the same sentence as players like McEnroe, Sampras and Agassi is a great honour but I still have a lot of work to do."
Last year was something of a breakthrough for the Florida-based Harrison. He cracked the top 100, battled through qualifying at the French Open and Wimbledon (before losing to Robin Soderling and David Ferrer respectively) and became the first American teenager since Roddick to reach back-to-back ATP semifinals.
He also demonstrated his fighting spirit, winning matches after losing the opening set on 15 occasions.
"It was a very big year for me in terms of experience," says Harrison. "I was able to play the main draw of all four grand slams and play against a number of top 10 players including the best - Roger Federer. I have a lot of work to do but I took a lot of good things from last year and hope to make them better in 2012."
Harrison has an irresistible work ethic, drilled into him from a young age by father Pat, briefly a Challenger-level professional and for a long period his coach. Before the age of 10, Harrison was waking at 6am most days, hitting 5000 balls a day when home schooling didn't get in the way.
"I definitely learned this from my dad," remembers Harrison.
"He taught my brother Christian [currently playing on the ATP junior circuit] and I that if we want to be the best, we have to put in the work. Talent alone gets you nowhere."
At the age of 11, he reached the final of the Shreveport City Championship in Louisiana and his opponent was his father. Ryan slept in his parents' bed the night before the match - in an attempt to disrupt his father's sleep.
Pat still won 6-3 6-1; Ryan abused the umpire at one point, was eventually admonished by his father and left the court in tears.
"I was disappointed that I lost at the time but we laugh about it now. There was no chance he was going to just let me win," remembers Harrison.
This week will be his first Heineken Open, after he was granted a wildcard by tournament director Richard Palmer, who lauded him as an "outstanding prospect".
Harrison has a big serve and groundstrokes that have drawn comparisons with Agassi.
He says former Auckland favourite Isner had recommended the tournament but he got most of the inside information from Michael Venus, with the New Zealander a close friend and training partner.
"I have heard that the fans in New Zealand are great so I am looking forward to playing in front of them," says Harrison. "It is always a good feeling to play in front of an energised crowd."
With Harrison, energy looks to be guaranteed.
