There's this urban legend that's rather disturbing, since most of these kinds of stories have a small root of truth. Although this one is a myth and was used in horror movies, the story is very likely to have happened. Basically because it's not another spooky story about a ghost showing up in a haunted house.

If you believe the story, there was a woman showing up in broad daylight and followed children that were unattended. She was wearing a mask on her face and asked the child if they thought she was pretty. If the child responded "no" the woman would kill it. If it replied "yes" the woman would take of her mask and show the child that her mouth was cut open on both sides. She would ask the child if they though she was pretty now. If the child said "yes," the woman would mutilate its face with giant scissors (no joke). If the answer was "no" the kid signed its death wish.

The funny part is, there's supposed to be a right answer. Replying with a "you're average" would be a wise choice, which is recommended by the story tellers, if a child would ever meat this psychopath. The chances are some kid might go bananas later on in their life and remember the story. They'd cut their own face open and become part of the legend, since it's so cool and shit. You never know. Maybe there were cases of this thing happening. 

There's another weird theory about the encounter - if you give the woman some candy, she'll leave you alone. This sounds ridiculous and I'd like to watch her eat the candy with her face cut open - good luck keeping them in your mouth. 

There's at least 3 horror movies based on the story