Hi, my name is Maastricht, and I was, and probably still am, obnoxiously arrogant.
(everybody say: Hi Maastricht!" )
And you know what? I never knew I came across as arrogant. That’s right, no-one had taken the time to tell me in a constructive manner. All I knew is that I was a lot brighter then my parents, and brighter then most people I counted as friends. And the combination of intelligence and social isolation is self-reinforcing: no-one corrects you in your assumptions anymore, especially not when you’re wrong.
Let me give an example. It’s a warm, sunny afternoon late in September and I wait for the bus back home from work. My heavy wintercoat is draped over my arm. A teen next to me looks at me with roll-eyes and suddenly bursts out: “Why’d you bring that heavy coat? It’s warm enough to go out with just a T-shirt!” To which I replied: “Sure, but when I left home at 07.30 this morning it was just above freezing.”
He was genuinely surprised, that thought just hadn’t occurred to him. And if he hadn’t asked me, he’d might very well have lived on in the assumption that some people are just stupid cry-babies, irrationally afraid of catching colds even in sunny weather.
For lonely, arrogant people, (and many arrogant people are lonely) the explanation that people are " just stupid" is an easier one, then “maybe I’m not as smart as I think I am”. And if such arrogance doesn’t get properly corrected in childhood, it won’t be automatically corrected in adult life. Most people confronted with arrogance, like the posters in this thread, just prefer to roll their eyes silently at us arrogantio’s. But we don’t learn anythign that way. We have either have learned to tone down, or, we have learned to filter out the irritated glances other throw them, having convinced ourselves those glances must be caused by jealousy, or because " people are just jerks" .
So Gladstone, could you bring up the courage to tell your co-student, in a constructive manner, how he comes across? You would do him, (and the world who has to deal with him the rest of his life) a huge favour.
“Hello X! Say, I was wondering, could you help me with something? Whenever me or my friends hold a presentation I often see you rolling your eyes and whispering to the people next to you. And you know, that gives me an uneasy feeling, like my speeches are somehow not quite right. Since we’re in a class on public speaking and all, could you tell me what you think is wrong with my speeches? I really want to better my performance, and I’d appreciate your input.”
All of this delivered in a sincere, friendly tone of voice, of course. He’ll probably turn red and walk off stammering.
Really, in this way, you’ll scare the shit out of your classmate, you’ll give him a lot to think about, and best of all: you’ll be impeccably polite. 
Of course, if he responds with pointing out to you all he thinks IS wrong with your speech techniques, then the guy is beyond help and deserves all he’s going to get. 