Have to go with School Days. And not for what you'd expect.
What bothered me the most about it was the obnoxious fanservice. It would have been okay if it weren't for that… But the fanservice was excessive.
Anime with fanservice does not always bother me, it's just when it goes way out of it's way to bring constant fanservice, and that's exactly what the first half of School Days did. The last half got better, but then there was... the ending. Which was just a little too twisted for my liking.
Seriously, I was just sitting there shaking my head in how ridiculous all of the fanservice was, and it happened all of the time! I know the anime wasn't targeted at me... But seriously, what guy wants to see anime girl panties and boobs? Geez. I'm just like "Couldn't you be using this time to be showing us something more useful to the plot?"