Generally speaking, inviting a guy who goes by the name “Killer Joe” into your home is a spectacularly unwise idea. Then again, the characters populating this unhinged slice of depravity from William Friedkin could never be mistaken for Rhodes scholars, or even elementary-school graduates. They are breathlessly stupid people snared in a web of their own stupid decisions, and Friedkin shows them no pity. He is particularly malicious toward Emile Hirsch’s trailer-park drug dealer, a deep-in-debt Texas lowlife who hatches a woefully ill-conceived plot to murder his mother and collect her life insurance.

In the span of about 20 minutes, Hirsch has the crap kicked out of him by mob enforcers, a gun shoved in his face by a naked Matthew McConaughey, and his skull nearly caved in via repeated blows to the head with a can of pie filling. But the director saves his greatest act of degradation for Gina Gershon. Let's just say KFC stock is likely to plummet in its wake.

At age 77, Friedkin has ceased giving any semblance of a fuck. Such depreciation of regard for social decorum is common in folks who reach a certain advanced age. For the average senior citizen, it might manifest in, say, a tendency to back out of driveways without looking. In Friedkin's case, it means making a movie like Killer Joe. 

Adapted from a play by Tracy Letts, who wrote the screenplay, it is maybe the most skin-crawlingly nasty picture to come from a major American director since David Lynch's Blue Velvet. Set against the burnt-out landscape of the American Southwest, in an unnamed town on the outskirts of Dallas, it indulges in the ugliest of "white trash" stereotypes. Gawking at one clan of slack-jawed, dirt-poor rednecks in particular, the movie wrings scum-black humor from yokels hee-hawing at televised monster truck rallies and attending funerals dressed in ripped suits and baseball caps. So mentally and morally destitute are they that a contract killer with a fried-chicken fetish comes off looking virtuous. He's been hired to snuff out the family matriarch, but Friedkin has condemned them all to death, in a climax wet with blood and sexual brutality. Then, in a final twisted joke, he fades to black and cues up Clarence Carter's hysterically horny "Strokin'."

If Killer Joe were the product of a younger filmmaker, the cruelty and condescension would translate as desperately attention-seeking. But Friedkin has been pushing, prodding and provoking audiences for decades. If the provocation seems emptier here, that's because he has lived long enough to cast off the burden of restraint. Killer Joe has no underlying message to leaven and redeem the violence and perversion. It only has the visceral charge of a master shit-disturber going all-in on his basest instincts. As a primal gut-punch, the movie can't be called anything other than a success. It's disgusting, but just try looking away. You can't.

Let's not misrepresent the film: It isn't torture porn. While much of its imagery is certainly gratuitous—Gershon's pubic hair appears before she does—the film earned its NC-17 rating more for how icky it feels than anything it depicts. Even if Friedkin edited out Hirsch's bludgeoning or that queasy scene with the chicken drumstick, the movie still would've been slapped with that damning rating for McConaughey's performance alone. He finds his best role yet as the titular Joe—lawman by day, hitman by night, intangibly frightening always. He slithers across the screen draped in leather, his mouth agape, hiding derangement behind a cloak of gentility. Eventually, he wraps himself around Juno Temple, the movie's lone symbol of virginal innocence, in a scene that ends up only the second-most disturbing in the film. McConaughey gives himself over so completely to sleaziness that, like Killer Joe itself, you can't help but admire him for it. 

Critic's Grade: A-

SEE IT: Killer Joe is rated NC-17. It opens Friday at Fox Tower.