I hate finding mistakes by the typesetter. Why can't that person just leave it the way I had it and not introduce such obvious errors?! It's not their job to change things!
I hate finding mistakes I've made -- why didn't the typesetter realize I meant to put that title in italics and fix that for me, instead of leaving such an obvious mistake? Why can they never show a little initiative?!
I hate finding grammatical errors. Why wasn't that caught at the copy-editing stage? I find this especially irksome on books where I was the copyeditor.
Worst of all is how correcting galley proofs makes me fat. I can only stand the intense tedium of reading text letter by letter for an hour or so before I have to take a break. And sitting in my office, resisting the obvious siren call of Facebook and Twitter, the only alternative is the coffee shop downstairs. Damn them and their lattes and giant cookies!
800 calories later, and I'm still only on page 35.