OBCO
A person who gets so wrapped up in a game they act like the world is ending if they don't win. Some take medicine to stay sane, others just get beaten up by their friends.
''If I don't get first place, I'll quit the game and you'll regret it!''
''You said you'd help me beat this boss! Now you're just standing there!''
''I'm not done with this dungeon yet! You can't just leave!''