What can be done about a bully?

Tell someone. Find someone you trust and say something. Keeping it inside does nothing. Depending on the context, find out what resources you have at your disposal to stop the bullying. DO NOT TAKE THE LAW INTO YOUR OWN HANDS.
Every public school . in the U.S. is required to have anti-bullying policies & procedures. Document all episodes of bullying with dates & alleged perpetrators. Discuss with the school principal & counselor. If you feel their response is inadequate, contact the school district's psychology department. If all else fails, file a formal complaint with the school district's legal department. The victim needs counselling. .
Be assertive. If victim: look and act assertive. If bystander: support the victim, be assertive. If parent: support the child and help them feel safe and provide hope. If teacher: respond immediately and investigate any/all rumors of bullying. Check out www.Bullyfree.Com.