Hmm, let's see...
- People who cannot communicate their point of view in a coherent or inoffensive way and then resort to phrases like "you don't tolerate my opinion!" when everyone keeps telling them that they're full of shit.
- Forum staff that is lenient on trolls. I've seen whole communities go down this way: Some guys flame-bait and insult other members on a regular basis and the mods remain reluctant to even issue a warning and never resort to a healthy old-fashioned ban. I don't mind some discussions becoming more heated and rougher than others but if there's really no corner left on a forum where basic manners prevail, I'll set sails for more civilized shores sooner or later.
- Browsing the GFF without being logged in, because of those damn, bloated banners in everyone's signature. I'm glad there's an option for this in the User CP.

And while I have to agree that people who are overly anal about spelling are annoying, I think a complete lack of some of those basic qualities (spelling, grammar, punctuation...) can be even more unnerving.
Jam it back in, in the dark.