One of my favorite movies is Fight Club. It's gory, it's grimy, but it's also funny. One of the funniest scenes is the scene where Tyler Durden (played by the delicious Brad Pitt) explains to the Narrator (played by the un-sexy, sexy Ed Norton) how to make soap. He renders tallow, er fat, by.....Well check this scene out for yourself.
If you have a weak stomach or no sense of humor, you may not want to watch this.