Yeah, there's a few things I forgot. Some are sort of NB/Shoddy issues too, it's hard to keep them separate.
People who txtspeak, chatspeak, 1337speak, tYpE lIkE tHiS, TYPE IN ALL CAPS, speak foreign languages, or speak nonsensically. This makes your posts harder to read. If you want to emphasize something, don't use caps. This is the reason bold is there. If you are more comfortable speaking a foreign language, go to a forums/server in that language.
People who rate like veterans but have never played a competitive match. I was once one of these a long time ago, but look at me now. These can be trained away from it without flaming. Flaming turned me into an anti-flame vigilante and makes those who are of weaker will cry/quit pokemon forever/etc. I learned more on PR before they started flaming me than after. Flaming does not help people learn, it only makes them angry.
People who say "you're stupid" but offer no reasons why your way is wrong and their way is right. Even if your facts are wrong, having wrong facts helps us prove them wrong.
People who act like anti-flaming players are worse than those who support flaming just for that reason.