ANDY'S ANSWER: There is a difference between being teased and being bullied, although sometimes they feel like one and the same, especially if it's embarrassing. Generally, I would say that if it's someone that doesn't know you or doesn't like you, it's bullying, If it's someone that does like you or knows you like friends or family, it is probably just teasing.
Being teased is meant to be playful, and is never mean-spirited. It's best to treat it light-heartedly and find something to tease the other person back about. If a friend is teasing you and it really hurts your feelings, you need to tell them in a joking kind of way, "You know, I'm kind of sensitive about that and I would rather you don't pick on me while I'm in my vulnerable pubescent stage of life." I'm sure in 3 or 4 years that won't bother me, but I seem to be rather hormonal right now and none of us wants to see what happens when that gets unleased."
If it's just teasing, they will get the hint and stop.