August Underground's Mordum

"Mordum' is a home movie shot by serial killers. Peter Mountain, his Sadomasochism girlfriend, Crusty, and his depraved man-child brother, Maggot. After Peter walks in on Crusty and Maggot having sex, an argument erupts between him and Crusty. It is quelled when Crusty sexually arouses Peter and herself via self-mutilation with a piece of glass. The two then break into a crack house, where Peter beats the owner to death with a hammer.