Summarize:

Often, the underlying cause of bullying is feelings of inadequacy when compared to the other sibling. Perhaps your brother or sister thought your parents liked you more, and they became jealous as a result. Or your sibling may feel that you were more popular growing up or that you had an easier life. Think about what your sibling has experienced in their life and if that might contribute to them being angry or resentful. They may have chosen bullying as a way to get back at you for what they believed to be unfairness. Talking with your parents or other siblings may help you discover if your sibling felt this way about you. They may be able to give you the details and information that no one else can. There may be a chance that you unintentionally pinned yourself as the victim. Maybe you thought ignoring your sibling's behavior would cause them to stop, but it actually encouraged it instead. Or maybe you have played along hoping that by seeming unfazed, they would lose interest. Your sibling may not understand how much their words and actions hurt you, and continue to engage in the damaging behavior as a result. Those closest to you and who are familiar with the relationship may be able to give you insight as to whether or not you made it seem that the bullying was acceptable. Having this outside point of view that is removed from the situation is often what you need to find the truth. You may find that the most helpful answer comes straight from the horse's mouth. Ask your brother or sibling why they treat you this way. Although they may deny the behavior or shut down about it, you may get an answer if you probe long enough. You could say, "I feel like you criticize me and put me down more often than not. Can you tell me why you do this? I don't want to start an argument, but I would really like to know what happened to cause this behavior." Being honest with them may encourage them to open up to you. If you want your sibling to be honest with you, then make sure that you do things to facilitate honesty, such as by responding calmly, listening, and trying to understand them. Ask a therapist or look for books that discuss why bullying occurs. This may make you understand where your sibling is coming from. Understanding the root of bullying may help you resolve the conflict with your brother or sister. If possible, find a book that is written by a current or former bully. Even better, try to find someone in your life who used to be a bully but has changed their ways. Ask them questions about why they chose to exhibit that type of behavior and you may get a better idea of how you can fix your relationship.
Look for signs of jealousy or resentment. Examine your role in the bullying. Ask your sibling about their behavior. Conduct research about sibling bullies.