10. Billy's Too Obvious - Scream
Scream is a headf*ck of a movie that knows exactly how to manipulate its audience both by adopting and simultaneously skewering genre conventions as part of its self-referential storyline. Every time we see a cliche, we're supposed to recognise it and dismiss it or embrace it accordingly.
So when someone says they'll be right back, they won't and when someone is established early as a prime suspect, there's no way they're the real killer. Which is the case for Sidney's boyfriend Billy, who is way too obviously set up as the killer. We're told to believe it's a Red Herring, and we all did precisely that.
What Actually Happened...
And wouldn't you know it, it turned out that Billy genuinely was the killer, who was self-aware enough (and meta-aware enough) to set himself up in order to rule himself out. In reality, he and Stu were the killers who went to extraordinary lengths - including faking Billy's death - to throw everyone off the scent.