When is a friend not a friend?

Today is my birthday, and I've got several birthday wishes via the Uni of Queensland ITEE dept alumni social networking site.... so I went and updated my profile there today, and added a bunch of "friends" to my friend list. I always find the term "friend" offputting in social networking sites, because I find myself incapable of hooking up with people who might well be legitimate, or useful contacts for a particular site, but I don't think of them as friends. e.g. I wouldn't add some academics as "friends" on ITEE, because they're not... they're former teachers or colleagues who I respect (but don't really like) and would be good contacts on that kind of site.

I also sometimes want an "enemy" (or anti-friend) feature. There are just a couple of people on the ITEE site who I could happly tag as "enemy", and hope for a feature that (at least) makes me invisible to them. Not naming any names... but one has a hovercraft connotation.