Last week at work I came across possibly the grossest idiom in existence – 爪(つめ)の垢(あか)を煎(せん)じて飲む. The first thing I did was turn to my trusty 慣用句 (かんようく) online dictionary. The interface could be better; the search engine is pretty good, but if that doesn’t find it, you have to narrow down the idiom by the first two kana via the menu on the left. Some of the idioms have their own pages, others are just given on a long page with other definitions. The best part is that the whole thing is in Japanese, which forces you to study and get a feel for how it works in Japanese, rather than learning a straight up translation.
This one has its own page, and the definition is: 優れた人の爪の垢を貰って薬として飲むという意味で、その人に肖（あやか）ろうとすること。
So, yes, you boil an awesome person’s fingernail crud and drink it as medicine so that you can be cool like them. Something like that. I had to look up 肖(あやか)ろう, and I think it means something like “be lucky.” Still getting used to the usage here, but I’m thinking it’s something like “I wanna be like Mike.” It can be put into basically any tense by changing 飲む – some of the frequently used tenses are 飲みたい, 飲ませる. The difference between these two is pretty drastic. With 飲みたい, the speaker thinks the person is so great, great enough that they’d drink their fingernail crud. With 飲ませる, someone is clearly lacking something that crud from fingernails of superlative person X could hopefully fix, and the person doing the causing thinks they should drink up. Gross.
Here’s a blog entry with actual usage. Always good practice to learn stuff.
It would be fun to write a fake article about the “recent boom” of Japanese “fingernail crud cafes.”