Mom gets mad at uncle for enforcing the rules of his house with her 11-year-old son while the boy is staying with him and not letting him keep his PS5 in his room, and making him share with his cousins: 'He just didn't want to share the system'

"My house, my rules" is something you probably heard your parents utter at some point during your childhood, at a moment of deep injustice when you felt your rights weren't being recognized. But, as the adults in the situation, that was their prerogative, and that pet, or gaming console you wanted, or party you wanted to go to would have to wait. 

It's a little different when you're watching someone else's kid; you do need to make sure you're not imposing some rule on them that is egregious to their needs, upbringing, or sensibilities of their parents. Certainly, bringing your PS5 over to your uncle's house and trying to put it in your room when your cousins aren't allowed to have their gaming consoles in their rooms isn't a part of this equation. At any rate, it would have made more sense to just leave the PS5 at home, especially if the point wasn't to share it with the cousins. 

Beyond sensibilities and egregious rules, "My house, my rules" still applies. I'm sure we also remember going over to our friends houses and being surprised when their families did certain things completely differently and had a complete different set of rules than our homes did and we had to temporarily obey them every time we were there until we were in the relative sanity of our own family homes. 

Even then, you'd think that if, as a parent, you didn't agree with another parent's rules, you probably just wouldn't leave your kid there in the first place.