Don't like the narrative of "everyone treated me like shit up until now so I'll treat every person I meet like shit as well", he also threatens to use violence to solve everything and gets violent when angry, probably because he learned it from his dad
Absolutely horrible for a kid to go through that, but it's tangible how the narrative tries to get the sympathy of the readers. While it explains his behavior, it doesn't justify it.
Don't like the narrative of "everyone treated me like shit up until now so I'll treat every person I meet like shit as well", he also threatens to use violence to solve everything and gets violent when angry, probably because he learned it from his dad