9. Mandy Was In On The Murders - All The Boys Love Mandy Lane
The Set-Up: one-time high school misfit Mandy Lane (Amber Heard) finds herself coveted by the popular kids as she grows into an attractive young woman. She joins her new friends for a weekend away at a remote ranch, where they come under attack from a hooded serial killer.
The Twist: it turns out that Mandy was in on it the whole time. The murders are being committed by her old best friend, in revenge for the way the high school alphas have treated them over the years
Why It Doesn't Work: The ending of director Jonathan Levine's 2006 debut feature reflects the problems of the rest of the film: it's trying too hard to be smart and edgy, when it's ultimately a very simple slasher.
It just doesn't make sense that Mandy would play innocent all the way to the end when she had her victims where she wanted them for so long, so far from civilisation.