If you haven't seen
Flame Warriors and
the Grand List of Forum and Community Laws, do so now. I've actually contributed to the latter (Reverse Briar Patch Rule, Skew Line Debate Rule, Visual Zombification Postulate, Killing Joke, McHabe's Rule, Hell Hath No Trollbait), but basically, those sites are so awesome that anything we do here will look feeble by comparison, and you'll love it anyway.
Regardless.
The Idiot Sewer If more than 20% of the users talk in chatspeak, and less than 10% use correct grammar, you've ended up in the Idiot Sewer. Expect that 10% and the people who think they're a part of it to go on about how "literate" they are, but really, if they were all that smart, they wouldn't post in a place where the vast majority of the userbase will completely miss the point of their posts.
(Pot meet kettle, by the by. I stuck around on Gaia for a good four years before giving up.)
Pot o' BileIf you say anything outside the norm in the Pot, prepare for a barrage of fail macros. If you hate spoilers, your pants will be spoiled off the first time you mention it. If you write like a normal human being, you will be told unequivocally to lurk more, until you absorb that you're supposed to tell whiners to go be "an hero", not, y'know, try to commisserate or help them in any way. (SomethingAwful is a peculiar case - given its trigger-happy mods and its active shunning of all things meme, you'd think people would at least be civil out of sheer terror. Not so.)
EsoteriaEsoteria was founded on a ridiculously narrow subject. Enthusiasm for remote-control cars, potted geraniums or Joseph Merrick - things no one in their right mind would make a whole forum about, but there it is anyway. Given that there's only so much one can actually talk about these things, expect the forum to garner new posts on a biweekly basis, if you're lucky. Esoteria, however, has a surprising longevity, certainly surpassing that of the forum founded for no better reason than to talk about everything.