Why is my brother so angry?

How old is your brother? If he's a teenager it could just be a hormonal thing. I would definitely talk to your parents about this and maybe you could all sit down and have a chat with your brother and tell him that you love him and that you are worried about him and hate seeing him this way. I understand this can be difficult because it might make him more angry but if he sees the effect his anger is having on his family then he might want to stop the anger and get better. Maybe there is something bothering that he needs to get off his chest. If he doesn't want to talk to your family then maybe suggest a councilor or therapist who he can talk to in confidence. He might need a way to vent his anger. Why not suggest he starts a sport such as boxing or karate so he can channel his anger into something constructive. This could relieve his stress so he won't be as angry all the time. Good luck xx