You'll have to take my advice with a grain of salt since I don't use social networking sites and don't have a clue about their particular etiquette (although etiquette might be lost on someone as intentionally hazardous as this former "friend").

The first things that jump out at me are the quickness of your action and the braveness of it. I would have deliberated about it for some time, and I admire that you came to a decision quickly. Even more, it strikes me as a small and quiet (the privateness of your message) act of bravery to (a) state an unpopular opinion (in the U.S., "ridiculing fat people is unacceptable" is a hugely unpopular idea), (b) call out a peer on their behavior, and (c) officially cut them loose.

I'm sure you're aware there will be collateral damage (depending on the maturity level of your social group, you might get obnoxious messages from mutual friends or a reputatation for being an unfunny humanist type).

All in all, I'm surprised by and impressed with you response. Personally, however, being the insufferably lecture-y academic I am, I would have tried to be less alienating in order to make it a "teaching moment." I probabably would have delivered a bried prospectus on the sociology of bigotry, on various masking techniques bigots use ("I just CARE about fat people's HEALTH"), etc.

My way is likely highly annoying and less effective than yours, though.

I would have posted a comment along the lines of... "Sthenno doesn't care for the ignorant and abusive opinions of young women who need to get their heads out of their asses and stop spewing dung."

It is quite in vogue to attack large people these days...and I plan on helping make it in vogue for large people to fight back.

Geez, though, from the Facebook angle, I know EXACTLY what you're talking about. There are people amongst my "friends" that I swear, if I hear ONE MORE BIGOTED THING out of their mouths, I am going through that list with a battle axe (sorry, Obama, a scalpel just isn't going to cut it) and deleting every last one of them. (Unfortunately, at least one on this list is a coworker, and no matter how many times his name pops up on my home page, advertising that he's donated money to anti-choice groups, I can't delete his sorry you-know-what.)

Ugh. Frustration.

You did, quite possibly, the MOST right thing you could have done. To let your "friend" know that you don't think that was acceptable, and to spare your own sanity.

I would have trolled their Facebook for anything they're probably insecure about and posted a passive aggressive status about it.

Okay, I wouldn't have, but it's always tempting.

I think you did the right thing. A lecture would have probably been ignored, and taking the high road is always best.

I would have double-whammied (being that it really bothered you enough to act on it instead of just de-friend). I would have sent the message saying "Not cool. Totally ignorant. Not in any way cool with me. bye" only more eloquent. I then would have made a status message along the lines of "Gular thinks that anti-fat postings are stupid and will defriend all people who make those statements because ignorance and bigotry are lame."

That way the person knows you're talking about them and you're getting your point across to a broader audience. It also might get you referenced on Passive-aggressive notes, which would at the very least amuse you.

I'm very impressed at how maturely you handled it. I probably would have been more public about it (i.e. posting it to her wall or as a status comment instead of a p.m.) which would have been potentially ass-biting.

I'm definitely down with everyone who said to post a rebutting status message. Just be prepared for some windfall if you have mutual friends.

Just remember that her hatred is probably based on her own insecurities. Not that that makes it OK.

To update the situation: I sent the message and she immediately wrote a message back (she is always on Facebook). She said something like "I would care you deleted me, but I have no respect for you anyways. I thought I had deleted you, thanks for doing it for me."
I wrote something equally snide back (essentially saying that I never had respect for her, I just put up with her because of our mutual friend, who she ended up really hurting anyways). I then blocked her on Facebook, so that neither of us can message each other. I think she no longer has respect for me because she stayed friends with my ex-boyfriend after we split up(who she had never said more than 2 words to in her life before the breakup). We have a couple mutual friends from University, but I don't think she would message them or anything. It's possible she is now saying bad things about me on her Facebook (trying not to let that bother me). She is the type of person to have 700 friends on Facebook, and I only know 2 of those friends, so she can say anything she wants really and it'll never get back to me (all these people live in a different city).

I hope this is the end of it! Thanks to everyone for their support so far!

I think you were brave for sending her that message. I'm not surprised that she reacted in an immature manner. My only suggestion would have been to explain why her original comment was ignorant. She probably doesn't see why it was, but then again she may not have read a longer message.

I've encountered nearly the same situation. An acquaintance and her friend were making some disgustingly racist comments on her status, I left a comment stating how horrified I was by these statements, telling them they were bigots, and suggesting they grow up.

Then when I deleted her, I had the irrepressible urge to see how they replied. They were something along the lines of, "She just doesn't understand our kind of humor," and "I'm not racist, I have Black people in my family." So ignorant.

Heh, I would have said something snarky about "You only hate fat people because you're secretly afraid you might be one." But that's because I like nipping at people's heels like that.

I experienced something similar when a facebook "friend" (really, a guy I only met a few times and haven't seen in years) said something really sexist about the female psyche on his status. It got me so riled up that I responded immediately, telling him that I was deleting him because of his sexist comment. Before I even had a chance to delete him, he deleted my comment, then wrote on my wall saying that he was glad I was deleting him if I couldn't take a joke. Because sexism is so funny, right?

I think the best thing to do in these situations is to let them know whatever they said is not okay. I know the guy I confronted probably didn't give it a second thought, but maybe someone will.

Facebook is extremely serious business!

I think it was an excellent response.
(And, seriously, I can't believe some people still think it's okay to use pathologizing terms like 'obese' to describe fat people; does your (ex-)friend also describe gay people as 'inverts'?)