If I had to guess why him, I would say he must have a low self-image and therefore is more vunerable. And, because he has been taught to consider others' feelings and not to hurt others, he doesn't fight back until he's boiling over (he first tries to ignore). Therefore, he is an easy target. Kids are less likely to start up with another child who might hit back or say something hurtful.
I'm at the point of telling him to say some hurtful things back, but not sure that is the best way to handle this situation. And, if I'm correct about his sef-image how do I boost it. He has not shown an interest in anyone thing that I can help him excel at. Thank you for reading this and I look forward to your advice.
It doesn't seem that the occasional teasing has made him a social outcast. The fact that these boys can get him to boil over and get him to "put on a show" is what has them repeating their teasing. I suggest that as soon as anyone starts the usual teasing, he immediately uses humor or a quick comeback; he can't expect himself to ignore taunt after taunt and not blow up. That's what he's wired to do now. I'd suggest something like, " O.K. I guess it's time for you guys to try to make me feel bad again," or "Can you just say all the mean things you always say in a hurry because I think the rest of us would like to get on with playing this game," or "Are you through, sure you wouldn't like to get in a few more cheap shots?" If bullies can't rile you, there's no fun in it for them and they move on to another. I'd also like to see what would happen if he challenged one of these boys to a test of brute strength, like arm wrestling or seeing who can force each other out of a circle like the Japanese sumo wrestlers do.
I wouldn't currently worry a great deal about his self-esteem being low, it's tough figuring out how to deal with these social problems. Let's see what happens with this change in his approach.