11) Breaking the scroll behaviour
Even minor stuff. G+, for example, defaults (or defaulted to) to an exceptionally narrow scrollbar, a conspicuous violation of Fitts' law: make your UI control widgets as large as possible to allow for easy access.
I can only surmise that a designer was using Mac OS or another platform in which gesture / multi-touch controls worked around the need for scrollbar access. With a touchpad-disabled, TrackPoint-equipped, mouseless laptop, this was a frequent frustration.
Fucking NY Times.
Even funner are pages where scrolling stops working entirely when the page is fully loaded. As in, I can no longer read the article or zoom. So I have to refresh the page and hit the "stop" button before it finishes loading too much (but enough to have the text on the screen).