Easiest way is to not deal with him. Tell him to fuck off, and that you don't want his feedback, and not to touch your shit again. If he has an issue with playing at the practicing at the same time, set times where each of you is allowed to practice. Your roommate sounds extremely insecure and immature, I'd keep an eye on my gear but you gotta just tell him to fuck off. No one needs destructive criticism when they're just trying to get better or learn.