How can i help my younger brother?

My younger brother plays call of duty chronically. After school and for 4+ hours when he doesn't have school. What seems to be happening now is that he curses and trash talks people with a mic and i think is somewhat of an online bully now. He used to be very social but now when i get home i usually see him bad mouthing another player on call of duty. When hes on he plays with his friends from school in a clan and they talk crap at everyone they play with, even before they say anything. Hes developed a short temper in the game and with our mom and I. I don't want to be too abrisive or in his face about it because then i will look like a bully. What should I do to help? Should I even do anything?