Well, I never really thought of it as a hierarchy but I do losely think of people in the following terms:
Friends with a big F
Friends with a little F
Acquaintances whom I like
Acquaintances of whom I have no opinion
Strongly disfavored people
People I don't know but would like to know
People I don't know and don't want to know
People I don't know and am completely indifferent of
People just sort of slot in where they belong, but this is the only heirarchy that I do--and I think I do it to protect myself...I've been hurt a lot in the past by people I thought were friends...
It came about in law school, before that I never really thought about it--maybe the hellish social nightmare that is law school requires this? I haven't really thought about it much since then, to be honest.