When you are coaching you should try your best to compliment, instruct, or criticize a behavior and not the individual per se. Tell your team that you expect them to communicate in the same way. While you can't be expected to control the external environment away from the gym where this young man no doubt gets ribbing, you can control the environment in the gym. Anyone knowingly who shows this type of behavior toward another teammate that is destructive will first lose playing opportunity. If the behavior continues they will loose the opportunity to play on the team at all.
Kids love to play.
If you take away that opportunity you can alter their behavior. Failure to do so will diminish your ability to control the team. You must be willing to do this even if it means setting down one or more of your best players. Don't do this in practice time, but in a private meeting away from the court. You should give them guidelines of what you expect in their behavior and treatment of teammates.