Finally I realized that he wanted me to sympathize with how he was feeling. Then we were able to talk about ways he could handle it. Then, let your child know that though he can't control what other kids say, he can decide how he wants to react. If the teasing doesn't get a rise out of him, then the child who's teasing doesn't have fun or feel powerful. Your child can focus on whatever activity he was involved in, or simply walk away.
Few retorts deflect taunting better than agreeing with whatever the teaser is saying.
Ask for help. It takes lots of maturity to stay unfazed by teasing. Affectionate joshing is a wonderful way to nurture a sense of humor, but let your child be the guide. If he reacts poorly, perhaps it's the subject matter. Don't joke with him about an issue he's struggling with, such as learning to use the potty.