Are you being too hard or too critical of yourself? Your dream may be showing you yourself in the form of a bully so you can see that you need to treat yourself better and say kinder things to yourself.
A bully can also represent someone else around you that you feel is too hard on you or too hard on others around you. Make sure you or your spouse is not being a bully to your children. Sometimes a bully in a dream can represent that you feel life is really beating you down lately. Now is the time to stand up and be stronger than ever.