Son has the opportunity to learn a few lessons about life and suck it up and try to repair this.
IMO he must recognize that the coach is going to be there and it is his ball club. Unless Coach is doing something inappropriate that would warrant a dismissal he is not going to change or go anywhere. So the player has to suck it up and deal with it if he wants to play.
It will not be the last time in his life he will deal someone that will not be of his choosing but comes with the territory AND he doesn't like. Teachers, bosses and In-laws come to mind for starters. Death matches every time you encounter someone that rubs you wrong is a tough way to live life.
I also don't know how much respect this coach as among the other coaches but if he is warning people off your son as "not worth it attitude" then your son is also getting another lesson. You are your reputation. Protect it, build it and cherish it. In the end your good name is among everyone's most valuable possessions.