S is for Serial Killers - My Friend Dahmer
Full disclosure, I haven't gotten to this film yet, but I have read the source material which is in the form of an excellent graphic novel. More sad than creepy, we're given the first hand awkwardness of a serial killing in the making. And if anything will make you a murderer with cannibalistic tendencies, it would be high school.
So don't be scared and don't kill small animals, just get a little baked and watch the fucking movie.