One nasty motherfucker of a movie, and I mean that in an endearing way. As carelessly un-PC as "Postal" or "The Human Centipede 3" in its quest to offend anybody watching, but also carries its fair share of suspense, scares, and sick-minded humor. The violence is by turns vicious, creative, and unexpected. And the trinity of genre muscle helping things along (Pare! Kier! Crampton!) is strategically distributed throughout. S. Craig Zahler, who lately has been doing dazzling work on epic-length…