To investigate the cause of desire in bullies, we'll do it in the context without God's intervention.
Therefore, it is not possible for one to just simply love to bully or enjoy the sufferings/shame of others. One only does so if and only if one has been treated likewise. I'm saying this with the presupposition that there is always authority of some sort in place to keep everyone in check.
The reactive attitudes towards being bullied can be seen in two categories, provided that God does not intervene:
1. challenge authority (like many liberals today, and I believe many eastern faiths are applied here as well.)
2. bully others (twisted sense of justice)
I use "God's intervention" instead of "God's existence" as the absence of controlling factor because we are all built in God's image, hence the question to God's existence is already settled.