He clearly reached a point where EVERYTHING was a slight. Many of these instances weren't even intentional. I started reading his manifesto, and even at an early age, he was angry, jealous etc., over the smallest things. The story he recounts about purposely not inviting that one boy from his first grade class b/c he didn't like him, showed a vindictive streak at a very early age.
Of course all of this is written through his 22 year old self's hateful, and bitter eyes, but even then he took steps to "punish" those he didn't like, and felt satisfaction in doing so.
Based on the manifesto, the only thing I'm questioning right now regarding the parents is why the custody was so equally shared. He seemed to really prefer his mothers household, yet spent equal time at dad's. That's generally a good thing, but it seems dad was rarely around. Why have the kid stay with the dad when the reality is that he is with the girlfriend, and/or nannies? Why not have the kid go to dad's when the dad is actually there?