In my endless Yo-ji-juku-go files, half of which I get from the lovely Ootao-san, I was starting to notice that so many of their meanings were meant to be used in negative situations: 前代未聞、for example, or one I'm saving for the future, which means a 180 degree turn-around, but only in a bad way. I mentioned this to her and she took it as a challenge. Since then, she's been supplying me with happier yo-ji-juku-go. I like today's especially because there are tons of opportunities to use it, and because of the contrast between the violent nature of the kanji, and the pleasant meaning.
One of the problems with learning these, is that I always try to learn the kanji and their meanings individually, so I can use them in other contexts, but for the yo-ji meanings, it can be confusing. Brett's first post (cut-polish-polish-polish) can attest to this. So my first attempt at translating this one, according to the meaning of the kanji was: a laugh that rips your face open.
1. Smiling from ear to ear
2. A broad smile
My translation problems, as you can see, were two-fold. One is that 'laugh' and 'smile' are the same in Japanese, and you have to know the context to know precisely which one, although in some situations, it doesn't matter. The second is that the 破 character, which by itself means all sorts of violent tearing and ripping stuff, also lends itself to the concept of ほころぶ, which can mean either to rip (as in cloth or a piece of paper), or to stretch your lips open by using your face muscles. Huh.
例文 (featuring Japanese ghosts!)： 口裂け女は復讐の鬼であるので、いつも討とうとしている。だが、誰かを見つけて、殺すことができると、満足で破顔一笑する。その笑顔を見らずに住めばラッキーだと思えばいい。
The Kuchi-sake woman is continously driven by a desire for revenge, but when she finds and kills a victim, her satisfaction shows in her smile. If you can make it through life without seeing that smiling face, you should count yourself lucky.
Check out the Kuchi-sake info on Wikipedia for some background on who she is in Japanese Legend and Cinema, but basically, if a girl in a mask asks you if you think she's pretty, say "Yes," and stick with that answer no matter what.