On the island, a hierarchy begins to form and Jack uses the name calling as a way to put himself in a role of authority. He pushes himself up by pushing others down. This indicates that he is emotionally immature and does not have the social skills to treat others with kindness. Jack's actions also show a correlation to the outside world's power dynamics during the war.
The boys are mean to each other because of the lack of adult authority, as well as the harsh social environment causing