I've been called a bully
Being called a bully means that someone is telling you that your behaviour is not okay. That’s because bullying is a serious issue that can cause all people involved - the person getting bullied, the person doing the bullying and any witnesses - real harm.
For the person being bullied it’s a very stressful experience that can have a serious and long term impact on their life. It also can cause stress for the people watching it, who may feel helpless and afraid that they’ll be next.