Excellent post, furcoat. I would add:
It's a sofa, not a settee.
It's a sitting room, not a lounge.
You must never eat/drink whilst walking in public (apart from at horse shows when it is de rigeur)
Never ever clean your landrover
Flower is not pronounced the same as flour. You should say flaaaher.
You can only reply to invitations in one set way and in writing.
Mobile phones are common.
Colour TVs are pretty common too.
Satellite tv is utterly naff (not that it had been invented when I was a child but it's my parents' view now!)
Always ALWAYS write thank you letters.
Never say pardon.
I'll keep thinking .....