I did not occur to me that my idea of common courtesy may not be common after all, until my son questioned me in all seriousness, "why", and I didn't have a clear answer, except to acknowledge that I assumed too much. For example, my idea of respecting the elders isn't as common as I thought. I, as a apparent should actually teach that concept to my kids.
They agree or not, act or not is up to them, at least they hear it.
This is not license to scold kids. Just my observation this Sunday Monday.