There is a non-zero set of people in this person's life who will necessarily decide this person is an asshole anyhow. In the early days, you invite this person to social events, and they decline because they're practicing. Maybe someone's even crushing on this person and consistently asks them out and consistently gets declined. However polite they are in declining, there's one person who is going to decide they're an asshole. Whoever it is in second place on the team, who under normal circumstances would talented enough to be the star player on the team but is getting shown up by the fact they're on a team with Michael freakin' Jordan... they're likely to harbor opinions of assholery, because if we humans are good at anything, it's rationalizing our pre-existing beliefs and finding reasons why we're right.
When professional and financial success is obtained in later years, people who want a piece of it but are denied will decide this person is an asshole. A coach who tries to control this person to take credit for their fame but is rebuffed because what the coach is saying to do is not what it takes to be great will decide this guy is an asshole. The reporter who tries to weasel their way in to hitch themselves to this rising star and asks for interviews but gets rebuffed because it's not what is necessary to become great may do a hit piece around convincing everyone they're an asshole.
And so forth and so on.
On the Internet, if you simply express a strong opinion, of any kind, no matter how politely, some subset of people will take as proof you're an asshole. If someone posts disagreement and you decline to instantly and totally agree with that person, a somewhat larger group of people will decide you're an asshole.
The upshot is that there's two different kinds of assholery; actually being a jerk, in as objective a sense as possible, and people who will decide you're being an asshole because you've done things that are (again as objectively as possible) not assholery, but because you are resisting doing what they want or some other thing that is really entirely on them.
From where we sit at a distance, it is often difficult to borderline impossible to tell which is which, or to tell the difference between a genuinely nice guy and someone who got advised to hire a PR firm.