Online: Pm's. There is nothing worse than getting online, and having a shit ton of pm's that the person could have just made a thread, but instead they pm me thinking I am a timeless person, and can answer every question they have to ask me, when they could just post a thread, and get the answer faster, and by more people. Possibly even a better answer than what I can offer.
Offline: People who are annoying, or yell when they talk, and they think they are just talking regular however they are really yelling. Fucking the worst thing ever...