“Assassination Nation” is a bloody, ugly, stomach-churning, mesmerizing film. It also may be one of the most important ones this year. Despite the way it was marketed, this isn’t a female-fronted knockoff of the “Purge” series: instead, what starts out as a teen comedy quickly mutates into an incendiary social satire about the horrors of cyber-mobbing and the paradoxes of modern life.

As the film opens we meet Lily (Odessa Young), a talented but rebellious senior with some subversive ideas about the culture of her school. It soon becomes clear that Lily’s leading a double life: she’s not only holding down a high school relationship, but flirting heavily online with someone much older. Things quickly escalate when an online hacker starts leaking, drip by drip, the townspeople’s unedited records of online activity onto the public Internet. Lily’s double life is almost immediately exposed—and what’s worse, another student’s testimony identifies her as the original hacker.

Madness follows. Death threats give way to rocks thrown through windows, nooses on streetlights, and knives in dresser drawers. (The movie is even set in Salem, Massachusetts. A little too on-the-nose? Probably.) To defend themselves, Lily and her friends grab their own guns and take to the streets. And as the film hurtles toward its violent end, Lily breaks the fourth wall and delivers a ferocious diatribe against the conflicting demands of 21^st-century femininity: “Be an angel. Be a whore.” It’s a hopeless task, so why not lash out?

This is what happens, director Sam Levinson tells us, when achievement-test culture and porn culture converge: young women are driven to “market” themselves in two mutually exclusive ways. The College Admission Brand demands wide-eyed innocent enthusiasm, perfect grades, pages of volunteer work, and the All-American look. The Snapchat Brand demands a level of nudity and self-degradation “hot” enough to compete with the airbrushed output of the San Fernando Valley. Fail the former, and doors to the future slam shut. Fail the latter, and taste the sting of social and sexual rejection. But above all else, the two brands can never overlap.

Certainly to some extent it’s an extension of the age-old tension between “respectable” and “cool”—but modern technological forces have pushed this into overdrive. When the ever-swelling demands of the College Prep World accelerate alongside the ever-more-deviant demands of a porn-addled male population, something has to give.

Such is the raging fire that animates “Assassination Nation”—and it’s fierce indeed. The power of the social critique here, though, extends well beyond dysfunctional gender relations: “Assassination Nation” is a deconstruction of the modern expectation that individuals conform in all respects to the filtered purity of their social media presences.

In a chilling early sequence—eerily reminiscent of the pivotal lynching account in Spike Lee’s recent “BlacKkKlansman”—a jeering crowd of white suburbanites accuses a respected black principal of “pedophilia.” His sin? Having bathtub photos of his young daughter on his personal phone, the contents of which are now strewn across the web.

What are the consequences, Levinson wonders, of a cultural moment in which an individual’s past actions—no matter how private or irrelevant to a given situation—must be dredged up and evaluated against a perpetually evolving consensus of “Good Person” norms? (Would you survive such an inquisition? Would I? Who can really say?) And the lurking, creeping dread inherent in those questions is why “Assassination Nation” works.

If Harmony Korine directed an episode of “Black Mirror” with input from Quentin Tarantino, something like this would probably result. That sort of thing obviously isn’t to everyone’s (or even most people’s) taste. But for those who like their social commentary steeped in striking imagery and pitch-black comedy, “Assassination Nation” is not a movie to miss.