What upset me so much that I reacted this way?

It was multiple factors, but what really set me off was whispered tells from someone nagging me about my healing assignments. And then pointing out that I always make the same mistakes with healing assignments. It's not that I can't take the criticism (which I normally can to a point) - it's the way in which it was delivered, the attitude behind it. It come to the point where I actually had to mute someone on vent, and was seriously considering putting them on my ignore list. This is a big problem when that person is someone with whom i actually DO need to communicate.

Look. I know you are just trying to help. I realize that when you explain, in great detail, over vent, repeatedly, every chance you get, exactly how, why, when, where, and WHO did everything wrong, you really are just trying to help us improve. I also realize that when you tell every single class how to play their class and ask why the &*%^ they don't just use such and such spell, and call them out for every mistake they make, you are just trying to be helpful. I know you are experienced and therefore you feel you have a right to talk non-stop OVER the raid leader. I know that when we mess up and you shriek into vent "SEE! I TOLD YOU SO!" that you are just.... well yeah i can't excuse that. You're just being a dick, sorry.

I will make another post about healer micromanagement, but right now I just need to vent. Why is it a problem when someone acts this way in a raid?

• You may think you are trying to help the raid, but what you are actually doing is trying to show your vast superior knowledge and experience. This is NOT for the good of the raid - it drags down the morale of the group as a whole, in order to raise your own individual self-opinion.
  
• The worst thing of all is that this RUINS focus. We couldn't get "in the zone" last night. I was a mess, and could not heal properly. People should have been topped off who weren't. There is no excuse for having 7 healers, and not having DPS topped off if they aren't doing anything wrong. Even Fulguralis noticed it, and normally he has both eyes staring greedily at the recount meter. (I'm just poking at you Ful!)
• If I were just another DPS, I could put the person in question on my ignore list, and mute them in vent. It's extreme, but if it's ruining my focus, and that person is not a raid leader, it may be the best thing to do. Unfortunately, as a healing lead, I really should not be doing that. I can't ignore you because if something DOES go wrong, I need to be able to hear what you may communicate.

More and more, this is leading me to a very drastic conclusion that I am loathe to accept. It may just be that I cannot raid with this person anymore. Usually, when someone says they aren't going to raid because of one individual, I have a "get over it" attitude. But when I'm trying to organize, communicate, and help lead, I can't just ignore them. He's been talked to repeatedly, and things change for a few days, and then go back to before and even get worse. I will even venture to say that at least last night he was telling me everything I was doing wrong via whisper. He used to just shout it out in vent - he's honoring our request to make it private, he's trying to improve, and it is still not enough for me.

If it's not a problem for anyone but me, then it is my responsibility to step down, to step out. This is my problem, and I should address it. And maybe the only way to address it is just to not come to the raid. It's not from some fit of pique, but more because I can't do my job, I cannot focus, and it upsets me far too much to be able to function properly.