Shins

Here's an interesting expression one of my student's taught me. Earlier this year, I was asking her what she thought of her new home room teacher. He seems like a genial chap so I thought she might like him:

"He's always smiling isn't he?" I said.
"Isn't he though!" says she, "I don't know what he has to be smiling about! He's in his late 30s and he's still すねかじり!"

Let's look at the kanji for that shall we:

脛　ー　すね means "shin"
齧る　－　かじる means "to gnaw"

Literally it means to gnaw at someone's shins, but idiomatically to sponge off someone, usually one's parents. Another oft-used word for this is パラサイトシングル or "parasite single" - somebody unmarried and still living with and sponging off their parents. Obviously, this particular student doesn't have a high opinion of her teacher.

There's one other use of the word 脛 idiomatically that is of interest:

脛に傷持つ　－　すねにきずもつ　－　to have a guilty consience or a shady past. Here's a nice example off of Jim Breen's web-dictionary.

すねにきずもつ者は他人の批評などしないほうがよい。
People who live in glass houses shouldn't throw stones.