In reply to Trangia:
> Other conventions I was taught...
When it comes to manners, to me there is only one important thing, and that is to make other people feel relaxed and comfortable. At times, this means throwing convention to the four winds, at others, following the rules to the letter.
Of course, some rules I don't even realise exist, never having come into contact with them. If someone considered me rude for not following a rule that I wasn't aware of, then that would be a bit closed minded of them. Maybe it isn't that they consider me rude, just uneducated (and so therefore maybe someone that they can enjoy looking down at).
If I met someone who wasn't aware of rules, then the polite thing to do in my mind is to make them feel completely comfortable about it, one way or another.