“Jennifer’s Body” is pretty straightforward in its intentions: mix this season’s hot teen genre, the vampire flick, with that old standby the high-school movie. Cast smoking hot Megan Fox as the bitchy bodacious queen bee, Amanda Seyfried as her nerdy best friend, and throw in some snarky teen-speak by screenwriter Diablo Cody (“Juno”). There’s your movie, no?
Well, maybe. Let’s start with Fox, an actress of great beauty and indeterminate talent (who at least has had the good sense to bail on Michael Bay after two “Transformers” paychecks): She’s cast here as Jennifer, a rapacious piece of high-school jailbait deployed in low-riding jeans and cheerleader outfits. Jennifer’s the type of girl who will grab the breasts of her mousy friend Needy (Seyfried) and tell her: “These are like smart bombs. You point ’em in the right direction and shake ’em, and things get real.”