“Hell is a teenage girl,” states a Sartre-wise inmate at Leech Lake Women’s Correctional Hospital. She’s Needy (Amanda Seyfried, “Mamma Mia!,” “Mean Girls”) and she tells us what happened back in Devil’s Kettle, pop. 7036, to her best-friend-forever Jennifer (Megan Fox) until a Home Depot boxcutter came between them. Jennifer is a stupid, sexy highschooler who suffers a botched satanic rite performed by a shitty indie band “from the city.” That’s what she gets for thinking Jesus invented the calendar and asking if a Sikh kid is uncircumcised like “a sea cucumber.” She seduces and sucks male classmates for her monthly intake of beauty blood. Director Karyn Kusama (“Girlfight,” “Aeon Flux”) lends no focus to the tone-shifting story by “Juno” screenwriter Diablo Cody. “Both horror and comedy require a storyteller who wants to manipulate the audience,” suggests producer and “Juno” director Jason Reitman in the press notes. “They are very close siblings.  I think they’re more related than other film genres.” That’s interesting, although it indicts “Jennifer’s Body,” where the horror is haphazard. The humor is better but that coupling is less sparky than an extremely close close-up of a BFF liplock with tongue. Lance Henriksen makes an uncredited appearance, returning to the Vancouver environs where Chris Carter shot so much of their “Millennium” Fox series. With Johnny Simmons, a bewigged J.K. Simmons, Amy Sedaris and Adam Brody. 102m. (Bill Stamets)