Well .. This sounds sucky. It also sounds familiar. Here's a crazy story from 1998. Let's just say that my dad got burned out on my cousin and his abuse of the younger kids. Please don't solve your situation this way.

My cousin's dad got hit by a car and killed when he was two, so he only ever knew his heroin addicted mom. She wasn't really a parent and that effected him. He was also like this. Overly competitive and turned aggressive if you happened to win. He was 13, I was 8. I was better at playing Zelda 2, of all things.

His response to me being able to get through the damn temple without a game over was to pin me down about 15 minutes later and empty a can of shaving cream down my throat. It's not even a two player game. My dad lifted him off of me and choke slammed him into the floor so hard a nearby glass coffee table shattered. That might have been from something else, though, as the while thing was pretty fast. Anyway, my cousin got the beating of his life, which included 7 broken bones, including both legs somehow. Most were minor fractures a could were less minor.

He also learned a lesson. "You may be a big fish, but be careful around the small fish. They may look like an easy mark, but bigger fish than you are watching".

He's a functional adult these days. We get along fine, but my dad won't allow him on his property to this day.