Get him back somehow, but in a friendly way. Kids rip on each other, it's what they do. It may have been something of a test, to see if you can fit in with their clique. I hate to say it, but in that case, well, you didn't pass. Hell, my friends and I insult each other all the time, sometimes gang up on each other for comedic effect, etc. We never mean anything by it, but it only works because we all understand that.
That should probably be added to the geek fallacy list somewhere; geeks often perceive insults as signs of disapproval and hate. While they can be, more often they're friendly, and serve more to bond two people; but they have to be reciprocal in that case. If one person is insulting another who isn't insulting back, then chances are it's not a friendly relationship. Also, insults of a friendly type MUST be to the person's face; saying it behind their back isn't friendly.
If someone insults you, read into how they do it, not just what they say; note their stance, tone of voice, etc. Really, you shouldn't even be paying attention to the content of the insult, it doesn't matter. If their delivery clearly has hateful overtones, or you think they're talking about you behind your back, then it isn't friendly banter; avoid them. If their delivery sounds jovial, or seems to be leading you on, insult them back in like fashion. Be careful though, some people have unexpected taboos on what you can insult them; stick to generic, less creative insults until you figure out those taboos.
Most importantly though, don't take it too seriously. Even if they do hate you, so what? Don't take their insults as suggestions (i.e. if they make fun of your glasses, for example, don't feel you have to switch to contacts). You'll have to figure out for yourself how to deal with the insults, but a starting point is to keep your sense of humor about things. You'll find that people respect wit more than intelligence, so if you can come up with snappy comebacks you will probably gain respect; hell, if you comeback at all you'll gain some respect compared to just idly standing there.