The Etiquette of Facebook Friending - is there any?

So, what's the etiquette of friending and defriending?  Sure, it's easy enough to ignore a friend request.  That person you barely knew in high school - or who barely knew you?  Just ignore.  Or accept and then block their postings.  They'll likely never know.  What about family members?  Some of us probably don't want our aunts, uncles, in-laws, 3rd cousin once removed to see what we post on facebook.  So do we have to accept their friend requests?  That can be hairy.  What about co-workers?  I did ignore a co-workers friend request.  It can be sensitive.  But accept the request - well then, best be careful what you post!  I try not to put anything on facebook I wouldn't say elsewhere - or at least I word my post such unless you really know - like you ask me - you don't know who or what I'm talking about, but I can still have my little vent or snark moment or share something funny, gleeful or joyous. 
What about the people you friended previously who are no longer your friends?  If it's just that you don't want to hear their nattering, you can block their posts.  I did this with one particularly obnoxious high school classmate.  He's the kind of guy who peaked in high school - and trust me, it was more of a bunny slope than a big mountain peak - but he really thinks he's all that.  So, I block his posts.  He doesn't know.  Easy.  Too bad they didn't have that lovely feature back when I defriended my husband's cousin (2nd cousin actually) and his wife.  Their posts were so extreme right wing, bigoted and hateful that I just couldn't stand to see them anymore.  So, thinking I was deleting one post from my view, I found out that I had just deleted the wife as a friend.  Well, her hubby soon followed.  And oh boy, that got me a vile e-mail from the cousin.  Suffice it to say he's not on the Christmas card list anymore!  An ignore button would have been easier and saved me his ignorant vitriol.
Now here's the real tricky part - what if it's someone you no longer want to see anything you post - no matter how benign?  Do you just defriend them?  Do you send them a nice little note?  How do you say "You made it clear you don't like me, so I'm defriending you" and do it nicely?  Is it worth the bother?  Really - they already don't like you - do you care if they don't like you more because you just dropped them with no word?  Or do you try and take the high road and be adult and own what you are doing?  Is it not being an adult to just drop them?  What's not adult about it?  What if you don't have something concrete as a reason - just a sense that this person lurked on your blog and talked about it to "friends" behind your back so that said "friends" would get upset?  How do you nicely deal with the situation?
All these etiquette problems that never existed before facebook!