Sorry to say that then you've become that FC's joke or meme, you could file a harassment ticket but since it's the FC itself, there's very little the mods can do (what? are they going to give a warning against EVERY MEMBER of that FC?).

I do think the "personal FC" is the best bet, like, if you don't like FCs because they can get clique-y and drama filled...uhm, generalization, much? yes, since the game encourages party play and forming a "tight" group (which...it's an MMO) some players in FCs can form their cliques and in large FCs those groups will eventually get fed up and leave to form their own, and not EVERY FC has drama (and if they do, it's not all the time) which is also fixed by making your own and being the sole member (I really see no drawback to this, really, it's all the pros you want and no cons besides not wanting to make one for whatever).

There IS also the option of joining one and just...turning off FC chat.