This is something I think I have adhered to in my adult life.
Did I do the same when I was younger? I can’t honestly say (or remember!).
My guess is that I did.
I was always brought up that way.
Be polite.
Say ‘please’ & ‘thank you’.
So do not all people? No, is clearly the answer otherwise this wouldn’t be a phrase.
The reality is, what would give you the right to treat someone any different than yourself?
Why would you?
We are all humans.
We all started off exactly the same.
The differences from then onwards are infinite & the reality is that most of that is by pure ‘Luck Of The Draw’.
So the second you think about treating someone, not as an ‘equal’…
…remind yourself not to be a dick…
…and be thankful for your luck in the draw of life & treat them the say way as you would like to be treated.