Small small text annoys me. So tiny that you have to zoom in. I use NoSquint to remember the text size for sites I go to. Web designers should set font size at 100% = 12pt = 16px so it starts out as readable. http://websemantics.co.uk/resources/font_size_conversion_chart
Really bad navigation.
Have a set end to the webpage instead of endless scroll. You know Page 1 then Page 2 etc.
Cookies used to track you so you see the same item you searched on hours or days ago over and over. Youtube showing me not variation but sameness until I delete the cookies.
Articles that are really ads. Kinda like those identity theft and gold ads on radio shows.
Example of bad website is http://www.yahoo.com
They do everything wrong. Only reason they are still kicking is name recognition. Once the ceo Marissa Mayer is fired you will changes.
Chrome has an interesting feature to address that annoyance.
The typical article page pattern is to have a narrow content column surrounded by ads and navigational junk on the left and right. The end result is that, if the page as a whole is comfortably displayed, the content column will be scrunched down to uncomfortably fine print.
Chrome's solution: The user double-right-clicks the content column. Then Chrome uses the click to figure out where in the page the content column is, it's width, etc., and zooms it to fit the whole window width. That almost always makes the text eminently readable and sometimes over-large. The user can then adjust the final size using two-finger squeeze / expand. Or alternatively, double-click again to see the whole page and pick a different spot to double-click and reapply the algorithm. It almost always solves the problem. It's a stroke of genius!