I was picked on quite a bit when I was a kid. Other kids called me "fag", "spaz" - and other things that don't take any originality or brainpower to come up with. If you are in school, and you have kids picking on you, I advise you to do at least one of these two things.
1. Don't let the insults bother you.
This is easier said than done, but remember this... the other kids are picking on you because they don't feel secure about themselves. They want to get you upset to make themselves feel better. If you don't get upset, they won't see you as a target.
As Buddha says - "If someone offers you a gift and you refuse to accept it, to whom does the gift belong?”
2. Insult them back with something funnier.
If you do this, the bully will be totally embarassed and probably won't be able to reply with a clever comeback. They may get mad and want to fight you. Don't get physical unless you absolutely have to. However, if your insult is clever and funny enough, other kids will very likely laugh and take your side.
Whatever you are going through, remember this: it may seem like it, but school is not going to last forever. Once you graduate high school, status such as nerd, jock - etc. means absolutely nothing, and you won't have to deal with those jerks ever again.