I don't know. As an adult, after having lived on my own, I'd ask if it was ok if I grabbed myself a drink when at my mom's or grams. Or ask if they had/have anything to snack on even if to help myself, so to speak.
I think it's the courtesy lead in, that I'd find bothersome. Plus reading about the bill from eating out. It's territorial, kind of, in an who's the eldest male. Denotes something deeper, as I think about this.

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