Oh for a world full of Indie girl bands. The trailers for Jennifer’s Body pitch it as a sort of X Factor or American Idol of comedy teen horror with all the vulgar trappings of the genre: overblown, gaudy and ultimately vacuous in its appeal to teenage pockets. It comes as quite a surprise when the film kicks in to find a witty, edgy horror outing possessed with an attitude of almost contemptuous throwaway transgression. Director Karyn Kusama (Aeon Flux) and writer Diabolo Cody (Juno) are responsible for what is, for half of its length at least, darkly humorous, suitably gory and great fun. And then, in the second half of the film, Jennifer’s Body bottles it and becomes just another silly teen slasher, opting for the get-out clause – on behalf of its seemingly glorious un-PC irreverence – of violence inflicted upon gals at the hands of unscrupulous guys.

Megan Fox (Transformers I and II) as the Jennifer of the title takes time out from being chased by giant robots to chase young men. The film opens with geeky bespectacled Needy Lesnicky (Amanda Seyfried) narrating our way from an asylum into her goggle-eyed high school life, aghast and amused at the antics of her dude-eating childhood friend Jennifer Check. It isn’t hard to explain why every stereotypical high school male, from the sensitive unassuming loser, Chip (Needy’s boyfriend), the lamebrain football beefcake and the guyliner Gothboy, drool over pneumatic cheerleader Jennifer, who has lips clearly tended to by the same bees that look after the femme fatale pout of Angelina Jolie. When a cool Indie band from the city visit the girls’ backwater town Jennifer seizes the chance to have some superior trouser fall under her willowy spell. Maybe it’s because Jennifer is so hot that she becomes the unwitting twisted fire starter, but, after one-helluva blazing venue, when we next see the dazed pom-pom girl she is not what she was. Or rather she is, only more so: a blood-sucking, flesh-tearing succubus who sets fire to her own tongue for amusement. The film is a Friday night fright ride. Although neither amazingly scary, nor revoltingly gory; nor, in its efforts to coin trendy catchphrases set to drive school teachers everywhere positively ‘freaktarded’, does it pall. The parts have so far added up to some satisfying, even radical American teen high school horror Math.

When Needy realises it is her own one-time stay-over girlfriend who is responsible for yucky teenboy terminations across the town, the stage is set for a showdown between the Best Friends Forever at the upcoming school dance. Jennifer clearly has her eyes and her teeth on Chip, and Needy must race to Buffy-style kick-ass rescue of the sensitive loser in distress. It is a refreshingly raunchy take on the genre, with a Gingery Snap to it, centering on the friendship of two girls who have been together ‘since the sandbox’, their friendship transcending those slugs-and-snails-and-puppy-dogs’-tails accessories called boys, who just happen to exist in a girl’s world.

Only when the film promises us a Carrie prom carnage riff as a climax, fatally it takes us bathing instead. Like the quality of the pun itself, it’s a damp squib. And before the bathing scene we get that lesbian snog, Jennifer and Needy playing ‘boyfriend and girlfriend’ like they used to. A lingering close-up moment destined for mega YouTube hits juxtaposed with Jennifer’s revelation of what happened to her on that fiery Indie band night. And it is here that in giving us balls, ultimately the film loses them. “Hell,” Needy tells us, at the opening of the film, “is a teenage girl”. But at a pivotal moment it is men who provide the hell, and this makes of Jennifer’s Body only half the irreverent, radical romp it was promising to be. Perhaps I’m simply too dumb to get it. Perhaps I just need to lighten up. Perhaps Rock music is just evil. Or perhaps Jennifer’s Body really is just the X Factor and American Idol of horror films and Satan really does work through Simon Cowell and Ryan Seacrest. Call me freaktarded, but oh how I wish Jennifer’s Body had been full of Indie girl bands.