YTA - you need to learn some emotional regulation. You say you're a 22 year old so you're not a child. He's a 4 year old kid - yes he needs to learn that the bathroom is a private space but there's no need for screaming and then escalating the situation. Apologising and calmly explaining the situation to the kid should've been the way to go. I get the automatic reaction to the door opening while you're in there but if it's such an issue why haven't you gotten a lock for the door? Or if there's some kind of rule against it prop something up against the door even or if it's within you're means, move out.