Actually, It has been studied(I can prove it) that adolescents and younger are quite influenced in violent media.They think its cool, and they want to do it . For example, there was 2 high school guys who decided they wanted to reenact a scene they saw in a game-in real life. Went riddling people with bullets, and were laughing. Got caught, and death penalty was given.
Now, I could be wrong, since usually my "resources" are unreliable. But that friend of yours........scary.
I don't think you should talk to him about it. He may be so far gone he might kill you too. So if I were you, I would move away to like, Cuba, so he would never find you. Start a new life.
Watch violence doesn't make you violent. If you want to imitate something tht you saw in games/movies it's because YOU have a mental issue, not something induced by them.
Oh yeah, run away from the problem seems like very.... BAD idea, it would be selfish to know something like "Oh this guy maybe is going to kill a half or a classroom, and I'm probably the only one that knows about this, but why should I care? Let's go to Cuba and have fun in a beach". Just no...