I think you should tell him that people bully others because they are weak in character. They don’t like themselves so they take it out on others. People who pick on the weak/small people who are very insecure themselves and refuse to recognize the vulnerable nature in all humans and that we are all the same. Everyone has their own demons they’re battling every day. Some people are insecure about their intelligence, looks, height, social standing or combinations of things like these. Sometimes people just want to fit in, so they do what everyone else is doing, just so they aren’t singled out and picked on themselves. Once I understood this, the mocks and ridicule of the bullying meant less to me. To me, it was just a desperate cry for help that was maladaptive.