Yikes! I am sorry you are having such a crappy experience with your classmates.
Save for a few of my classmates, most have proven to be nice, friendly and sane. The few that I can't stand either always have something to say and, of course, always say it with the tone of voice that says, "I know what I am saying is right," talk about their UG fraternity and are so impressed with themselves for the amount of drinking they did and still do or just naturally grate on my nerves. I have befriended a few people that seem to be solid citizens and just ignore the rest.