NPCs will always be nice to you, but in an MMORPG you play with real humans, so it's like living in the real world; there are nice people and not so nice ones.
DEAL WITH IT.
That's how this world is, and therefore how MMOs also are.
It won't help at all to post names on the forums.
People will still team up with them, either because they don't think they did something wrong or because they can get drops, exp or whatever by teaming up with them.

I'm not one of those people, I'm not even one of those who like competition in claiming mobs.
I get seriously pissed off when a party is not leaving the moment they see my party is already there, but I keep that anger to myself, and that's it.
You need to become thick-skinned to stuff like that.