Thanks for that link smiley. That page is excellent and resonates with me.
A quick example, one Thursday in September I was in Huddersfield on a work trip. In the evening I went to a pub - The Grove - where there was the weekly Irish Session. Huddersfield University (/gruff voice: "it were a Polytechnic in my day") has a respectable music degree and one of the new students had popped in with his violin. He didn't even sit down and listen, just took his instrument out of the case and played The Irish Washerwoman. OK, he could have picked a less cliched tune, but that aside, he was obviously a top class player, no doubt had been a child protege, and was surely used to accolades whatever and wherever he played...up until then. He couldn't understand how the reaction was precisely - nothing. Someone just struck up a tune and away they went. It wasn't rude or anything, I am sure they appreciated his playing, but, well, you get the picture.
I managed to have a quick chat, and although very much a beginner myself at the time (I still am) I knew a bit about etiquette. But that is a whole new subject. I tried to explain the reaction. I think had I known I would have simply directed him to Steve's page.