YTA Not going to get into a gun debate on reddit. But I'd like to ask. If the shoe was on the other foot, how would you react?

If your roommate came to you asking your opinion on something that you may or may not like that would add or change the lifestyle in the apartment, and you said you didn't care for the change and he went and did it anyway, would you not react the same way?

Not a debate but about the gun. You have no idea why he doesn't want to use a gun or want a gun around. It's not your business, he said no. Perhaps he had a bad experience, maybe it triggers something bad around being around a gun. Just because you warmed up to a gun at a firing range doesn't mean he will or feel like he should.

Imaginary scenario. What if you didn't like being around smokers, and he picked up smoking while you're there. Sure, he does it outside, but the smell is there and it lingers. Technically, he's not going to be breaking any lease laws, but it still drives you crazy. He didn't care because, hey because he can.

Honestly, the smartest things would have done besides it being on the lease, is to have a roommate agreement. Should have been discussed before moving it, it can signed by both signed and notarized. That way if he a conflict like this arises, you won't be the asshole.