Mine will probably be quite tame by comparison, but as I've gotten older I've found that I get creeped out by horror/slasher flicks more and more, and I pretty much avoid them entirely now. The most disturbing film that springs to mind for me is the first Cabin Fever. I remember stubbornly watching it from beginning to end, not being overly grossed out by the viscera (but it was pretty eww-y), but how everyone in that film is so quick to turn on and abandon each other and let them literally rot in a shed or something. For me, it was a genuinely disturbing and unsettling film.
I also remember seeing a low-budget, super-gory zombie flick in my early teens on the Sy-Fy Channel (back when it was still called the 'Sci-fi Channel') and there was this zombie with an exposed skull (which still retained its eyes) that camply shuffled around eating people's faces. Can't remember what it was called and I don't care to Google it, but I'm pretty sure that the zombie has become a minor meme now as I've seen it turn up in captioned images on forums and stuff. I have no idea why I endured the film all those years ago, it was pretty grim (in my opinion, anyway).
Oh yeah, and the Texas Chainsaw Massacre remake. What they did to that blonde fella gave me the chills.
No way I'm watching those Human Centipede flicks.