After leading this great rant on tiny type: I'm sick of your tiny tiny type I started thinking of other things that drive me nuts on the web.
Playing video/audio immediately. No, I don't want you to play that video until I tell you to. I might be at the office and piss off my many neighbors. I might be sleepy and want some quiet. Even worse are people who add multiple video ads to their pages. The only thing worse than two video ads is two video ads fighting each other for dominance. Do not play the video until I mash the play button. Yes, I realize that precludes video ads. I once visited a job recruiter site that immediately played audio that started "so you hate your job..." which is great at the office.
Block me from changing the font size. My eyesight isn't very good and I need to increase the size to read comfortably. Your great design is pointless if I can't read it.
Make your article be full width. Reading 100 words across is hard on the brain. I have a big display but I don't want to get a neck ache reading your content. There is a reason newspapers put text in columns.
Black backgrounds with gray text. Or dark gray backgrounds with slightly less dark gray text. Sure it might look cool but I read a lot of stuff on the web, and every time I switch back to a light background from the dark background my eyes bug out. Good typography is about good contrast. If you try read poorly contrasted text you will get a headache as your brain is trying to escape.
Too many moving things on your page. I hate being distracted with scrolling tweets, news banners, photo carousels and the like all trying to steal away my focus. You may as well just use flashing text again. I don't really like moving menus either, where a box of choices float up and down as you scroll. Sometimes it might be handy but mostly it acts like a bug crawling on your display. Squish it.
Chopping your article into 50 different pages. I am sure organizations do this to increase the ad views. At least some have a link to a full page view. Bless you.
Big things that happen automatically when you drag your mouse over them. Sometimes it's useful but if the accidental drag covers the entire page it's a sure way to piss people off. That goes for menus that contain a million items. Ever tried to find something in a single level menu that covers the page?
Settings that change on their own. How many times have I cursed Facebook's Sort menu? I want Most Recent damn you. Always.
Tiny type, but I can't beat the rant in the referenced article, and it had nice big type!