Mostly this. I visit a website to view its content, not its header. I don't need to waste 10% of the screen on something I will almost never use. On Desktop, I can press "Home" to get to the header in the rare instances I want to. On Mobile, screen space is even more valuable, so it's even more annoying to have to waste screen space on the stupid header (and no, web designers, the style that pops up and covers up the content you are trying to read when you scroll up one pixel is not a solution).
I just gave some thought to why it bothers me and I actually think some of it might be because they trigger a kind of "oh shit a 'search bar' add-on, kill it with fire!" reflex from the bad ol' days of most computers being full of malware and spyware (now the OS and most programs are spyware, so... progress?).
Of course the big ones are simply obnoxious wastes of space, and any that have a drop shadow on the content bother me for what seem like obvious reasons, but even the small ones bug me and I think that might be why.
[EDIT] That's just for the static ones—the ones that pop in and out based on scroll behavior are one of the worst design trends in the entire history of the Web, which is saying something, and are in an angry-making category all their own.
Mostly this. I visit a website to view its content, not its header. I don't need to waste 10% of the screen on something I will almost never use. On Desktop, I can press "Home" to get to the header in the rare instances I want to. On Mobile, screen space is even more valuable, so it's even more annoying to have to waste screen space on the stupid header (and no, web designers, the style that pops up and covers up the content you are trying to read when you scroll up one pixel is not a solution).
I'm here to read. Stop interfering with that.