I'm afraid this type of thing occurs in the UK too. Here in Manchester there are sessions where almost any ones welcome and ones run by "the exclusive brethren" as they are known locally. In fact these aren't really sessions at all but performances by people who hardly ever play with anybody else. They actively discourage people they don't know from attending and if new people do go they behave in an offensive ignorant manner until they leave. They seem to think they own the music (even though it was there before they were born and will still be there when they're dust). The worst aspect of it fore me is the way they treat beginners; with utter contempt. To me there is nothing more faltering than being asked by a beginner for help. I don't teach formally but if someone asks me for help I give it. This is not entirely altruistic I want to be playing in sessions into my old age(if I make it), with people of all ages like I do now. All the best PP