You're Wrong

That boy (or girl) you always see walking by himself... Yeah and I say "always" because he might be your neighbor or your classmate or you both live on the same street, anyways it's impossible to go a week without seeing em because they're somewhat part of your daily activities/routine.
Maybe one day you're with your pals, your click and he passes again, clearly sees your very much familiar face again but doesn't say a word again... You wouldn't have expressed how you felt if your friend didn't say "there he goes again, walking around thinking he's better than everybody" so that just ignited the fire in you and you say "You know I actually said Hi to him and the Snub just said Hello languidly and walked passed... there were people there and I was so embarrassed"
and that's how he suddenly becomes a subject for discussion.
You see we humans by default see things from our POV, we can't help it... Now that isn't the problem, the problem is–not seeing things from the other parties point of view after you've seen it from yours.
YOU'RE WRONG and your notion, hypothesis, theory and conclusion about him are all wrong too...
Did it ever occur to you, that boy that walks all by himself with his hands tucked in his pocket and face down might have a disturbing childhood, no one listened to him, no one allowed him speak freely, life forced him (at a very tender age) to deal with whatever mental/emotional problem he had all by himself. Hence, this is the only life he knows, a life where he is by himself and takes care of himself and even if he wanted to talk to you, he doesn't even know how to.
Or maybe it's like Jodi Picoult says

Bottom line: Judging or formulating theories about a loner won't stop him from being one. Loners are in a dark room all by themselves and couldn't get out even if they wanted to because they can't find their way out. Be the light in that dark room and they will come out. "how am I supposed to be the light?" you might ask, it's simple. Just be nice, be a friend, a true friend and it will naturally happen.
So next time you see him/her, don't judge, don't point fingers and don't label... You never know the demons people are fighting.