I think that an essential characteristic of bullies is sadism, sexual or otherwise, even if just to a small degree. Anything else is just callousness or assholeness.
sadism? Not sure, but I know my bullies were not driven by anything sexual.
That’s why I said “sexual or otherwise.” Sadism isn’t inherently sexual, it’s just usually assumed. A sadist can cause harm to people for joy, which is what bullies do, right?