I love figures of speech. Think of the visual possibilities of that phrase. Idioms. Colloquialisms. Regionalisms. Slang. All of those bits and pieces of everyday conversation that we accept as a matter of course define our background, our region of the country, our age. Cool. Boffo. Super. Sick. Rockin'. Neat. If I list many more, I'll be showing my age. As a matter of fact, these phrases show the age of books in which they're used as well.
I was reading a super funny book with a little boy I'm helping with his reading, and some of the "cool" kid dialogue was totally foreign to this very hip kid because its publication date was long before he was born. I had to explain what the terms meant. Not sure I did a very good job, because explaining idioms is like giving words to something you just KNOW. It made me think, however, that using the lingo that's in style and the hottest at the time you write your book isn't exactly a great idea. Language goes in and out of style as swiftly as shoulder pads and glittery lapels for women's suits.
Anyone remember The Little Colonel books for children? I rest my case . . .