Exaggerated: Carnegie is incapable of saying anything nice at all, and has a superpower allowing him to anticipate everything.
Carnegie is Proud of his intellectual gifts but not to the point of despising others. He knows his weakness in that area and makes a point of working on it. Those who know him don't feel him to be arrogant.
Carnegie's greater awareness of the world around him and/or the consequences of ideas and actions can lead to him being irritated by realities that are invisible to normal people. With no one to share it with, he becomes prickly.
Carnegie is brilliant, but has crippling self-esteem problems stemming from the constant mockery of his peers. In times of crisis, however, he is forced to offer solutions even though he's afraid to even speak.note Which can lead to a double subversion when he finally gets praise and recognition for his talents and doesn't know how to handle it properly.
Carnegie is smart, but convinced that he's an idiot.
Carnegie decides to become a nicer person...
Alternatively: Carnegie is only condescending to those he doesn't like. He's got a lot more patience for his friends.
Carnegie is socially awkward and puts up psychological barriers to protect his demand for autonomy. He is also aggressive in debate. Many mistake that for arrogance but those close to him know him as a Gentleman and a Scholarunderneath his shell.
...but gets over it.
... However, he's really insulting them on a higher level then they can understand, laughing behind their backs.
Carnegie make a show of being Nice to the Waiter. However he is really so arrogant that he cannot believe himself to be arrogant; because having a flaw would imply that he cannot control himself.
Parodied: Whenever anyone comes to Carnegie with a problem they need help solving, he insults them for several hours. When they finally get fed up and start to walk away, he says "Wait! Don't go! Here's the solution!"
Zig Zagged: Carnegie's niceness varies from day to day.
Averted: Intelligence is not a determinant of kindness.
Enforced: "Let's have The Smart Guy be a real asshole to everyone! That's how it works in real life, right?"
Lampshaded: "Ah, yes, your problem. Rest assured I've known all about it, long before you could even conceptualize it. By the time you started considering the possibility of a solution, I had already formulated several viable ones".
Carnegie has been an asshole all his life. He decided to start rigorously studying so that people would have to put up with him.
Alternatively: Carnegie, who has always been gifted with intelligence, is deliberately rude to people so that they will leave him alone.
Exploited: Ben, needing a partner for a science project, promptly asks the resident asshole.
Defied: Carnegie is told by those around him that they won't hesitate to kick him out if he doesn't shape up and start acting nicer.
Discussed: "Dammit, I wish there was someone else who could fix our problems. I hate going to that jackass for help".
Conversed: "Wow, that guy sure is a jackass. Why can't smart people be nice?"
Everyone that works with him hates Carnegie — he may be smart, but he's too much of an asshole to deal with.