Could my younger brother be a psychopath?

He is about 15 now. This is not a phase, he's always been quite stoic and unsympathetic. He's always been disrespectful to my mother... Just now, he kicked me really hard in the leg. Why? Because I squirted a bit of water at him. I think I may just bruise--and it's really hard to bruise me. -___- Just a week ago, when I was telling him about the Vietnam War and how American soldiers killed innocent children, most notably the Mai Lai Massacre. I told him how the hysteria over not being able to tell who was the Viet Cong got to them, and he said that he'd do the same. He said that , he a child is suspected of being in the Viet Cong, it's better to just kill all the children to get rid of that possibility. He looked totally serious. Even if he was joking, that's a pretty sick ******* joke. I've noticed that, whenever talking about people, he classifies them--either as smart, stupid, nerd, popular, ugly, etc. The only person that he listens to is my dad, and even then, he still calls my dad a ******* idiot occasionally. Also, he often says around me "Some people say I'm powerful", and although he may be kidding or just trying to get on my nerves, I feel like he says this too often....