I confess, I'm a scardey-cat, and I have the particularly unreasonable fear of ghosts, of all things. I managed to completely terrify myself into sleeplessness one evening by just reading the Wikipedia article about the Slit-Mouth Woman.
According to Japanese legend, the ghost of the Slit-Mouth Woman approaches her victims on the street, covering her mouth -- in the old days she used the long sleeves of her kimono as her cover, but in modern form she wears a surgical mask. She asks her victim, "Do you think I'm pretty?" A no answer means instant death; but a yes prompts her to reveal her face, showing that her mouth has been carved into a Glasgow grin. She asks again if she if pretty. Again, a no ensures instant death, but a yes this time means she blesses you with the opportunity to look as pretty as her, by slicing your mouth open into a similar Chelsea smile. In some versions of the story, she will also kill you when she does this.
The legend however does say there are ways to escape. The Slit-Mouth Woman, like many ghosts of lore, is easily confused. Simply repeating your answer multiple times, whatever it may be, can be enough to confuse her and allow you a chance to escape. Another (very Japanese) way to flee her wrath is to simply tell the ghost of the Slit-Mouth Woman that you are in a hurry and need to be elsewhere: she will apologize for her bad manners for detaining you, and let you be.
According to the legend, Slit-Mouth Woman was a beautiful girl whose jealous husband mutilated her face by slitting her mouth out to her ears. This trauma drove her to insanity, and this is why her ghost remains bent on inflicting the same fate upon others.