B.H.
My daughter got stabbed in the hand with scissors last year in Kindergarten and I've NEVER brought myself to forgive the brat that deliberately did it, and asked the teacher that my daughter not come anywhere near the brat which the teacher gladly did. Then the teacher actually suggested we have the girls seperated in different classrooms for first grade and things have been great ever since.
Some kids out there just have mean streaks or issues and in today's society noone will straighten them out so they continually get away hurting other's and never learn.
Keep your son away from him he'll just pick on your son or be a bad influence and change your sweet boy.
I've had another problem with a neighbor girl being really nice and a good friend to my daughter one minute and then ditching my daughter for another friend and really hurting my daughter's feelings repeatedly so I talked with my daughter and we had a talk about "true-real" friends and my daughter decided she didn't need her around anymore.