People that use the work "actually" twice in the same sentence.
Actually, I think we're even.
Mwa ha ha.
A thread in another forum reminded me of one thing that drives me stark staring bonkers:
When you come across a page by accident
:: insert obligatory nagvaaqtait reference ::
and start wandering around the site following links and reading other stuff-- and later when you want to go back to the original page you can't find the #### thing anywhere even when you follow every single link that's even remotely likely, and by this time you've forgotten what search term led you to the site in the first place, so you can't simply look for it again, and everything in your browser history takes you to the same wrong page, and...