Auto Page Jumping Web Sites
Those web sites which assume you want to jump to a new article as you scroll down drive me nuts, especially when I haven't finished reading the last paragraph and going back doesn't go back to where I was. And it then jumps to the next article again if I am not slow and careful when scrolling down to get to what I actually want to read.
And those sites which have slide-downs and slide-ups which get in the way of what you are reading when scrolling come a close second place in annoyance quota.
As do those slide-in-from-the-right frames which require one to take the mouse round the edge of the screen to actually scroll without permanently activating them and obscuring half the text one is reading..
Grrr.