Trolls. The people who essentially fight for the hell of it and add random stuff, like insulting someone's looks, even if that has nothing to do with the topic.

People who have a conflict with someone on the boards (knowing that this person reads the boards) and try to garner advice. It just has started quite a few fights that were ridiculous.

Cutesy typing. I understand spelling errors and not typing certain words. On another board I read, the moderator thinks it's awesome to write stuff like "dem", "dat", etc. She does it to be cute, and it's not cute. I also gathered that it's difficult for international readers to understand what the hell she's typing; I struggle with that sometimes, and I only know English.

I can't think of a word or phrase for it, but I read several boards about certain "famous" people or TV shows. The second that person makes it known s/he is reading the boards, the conversation goes sycophantic even if there were fair and valid criticisms of the person. It's really amazing. I don't believe people should be heartless and write cruel things for fun, but I really hate how good conversation is destroyed when people know that their words aren't going unnoticed by the person of the topic.

Crazy fans. You can write a fair and valid critique of a person and they'll jump all over you like you called their idol a pedophile. It's kind of scary.