I Saw the Devil (2010)
If you can't handle horror movies, DO NOT watch this film. This is one of the most violent, disturbing, and messed up tales of revenge in the history of film (that sounds crazy to say, but you should just watch to figure it out for yourself). After a serial killer captures and murders an ex-cop's wife, the ex-cop turns his life into a constant nightmare that he can't wake up from, he can't even die if he wanted to. Seriously, this movie is demented, genius, but truly disturbing. Proceed with caution.