I didn't meet any posh people until I was 19 and met my parents in law. First meeting was on their sailing yacht in St Malo harbour. Not knowing much about British customs, I was amazed at all the pre-lunch and pre-dinner drinks consumed( in cut glass, even on a boat). When asked ( on the first visit), what I would like to drink, I smiled at my lovely, charming future FiL and said, " Whatever you're having, sir". So I got drunk on pink gin first visit!
Don't know anyone posh now...but think that PiL were classy, rather than posh because they were very down to earth, ate left-overs, were frugal for themselves but generous to others, grew all their own veg, and polished their own silver!!