Very sleepy today but: very well put. I agree with the "people expect the rules of discourse to stay the same everywhere" thing as well.

I am far less 'nice' to many of my close friends, because there is less possibility of getting things confused, of us getting the wrong impression about the other, etc

Me too (I have an incredibly mean sense of humour, which not a lot of people see. Poor old Cam gets the worst of it :)). And on the other hand, I'm particularly polite to the kind of people who I know will react unpleasantly to being contradicted and I can't be bothered arguing with, and then they think I like them :/