The goriest film of all time has got to be Dead-Alive. It was made nearly 20 years ago, but no film has yet to come close. It has more blood and guts than Saw and Hostel combined. In fact, it's so over the top with the gore effects that it's impossible to take seriously, and it ends up becoming a comedy. Maybe that's why nobody has mentioned it yet, because it's so ludicrous that it's no longer gross.
As far as a film that had an effect on me, it takes a lot for something to actually gross me out these days (thanks, internet). I would say that one of the only films I've seen in my adult life that has made me feel ill is Deadgirl. Here's the basic plot. (WARNING to the sensitive, it's pretty sick) Two guys in high school go hang out in an abandoned mental hospital. They end up getting lost in the basement and find a storage room where there is a lone female zombie chained to a bed and left in the corner. Instead of getting the hell out of there, they decide to use her as their personal sex slave for the next few weeks. When one of them gets obsessed with it and invites all of his friends down there, you know that the only way that this can end is very badly. Like the human centipede, it's not too graphic, but it's the concept that's gross. Does it count as rape or necrophilia? That's a question I never thought I'd have to ponder before.
14 years