Hostel.
I love horror flicks, scary movies, etc. and I'm not particularly bothered by blood or gore ... but a movie that's all about watching people get tortured to death just isn't a fun time for me.
The later SAW movies get close to that territory, too. First one was good, Jigsaw was an interestingly twisted character, his traps were more about screwing with people and less about "lets watch someone's body get horrible mangled," and the twist ending took me completely by surprise. Correction: twist endings, plural. The whole last 20 minutes was mind-fuck after perfectly choreographed mind fuck.
For the record, I thoroughly enjoy the occasional "bad" movies that venture into "so bad it's good" territory. The Expendables, Will Smith's Wild Wild West, Street Fighter movie (fucking Raul Julia cracks me up) Manos, Plan 9 from Outer Space, etc etc etc .. all terrible terrible movies, but fun to watch and make fun of with friends.
The whole torture porn genre is just gross, not creative, not fun, nothing that movies should be, and it needs to go away, imo ... or be limited to direct-to-DVD snuff lite for people who are into that sort of thing.