夜郎自大

やろうじだい
yaroujidai

や　is for 「やった！」 As in, 「やった！このや行シリーズがやっと終わるみたい！」

Today will be the last Yojijukugo post that starts with や、ゆ、or　よ! Maybe not the last one FOREVER, but I think we've got enough to smack the smile off of any uppity bangumis that wanna tell us WE don't know Yojijukugo.

(Though, while we're still here, I'd personally like to request that Nirav make a KN^4 post on 余裕, cause seriously, that business is complicated!)

Today's entry is a great one to know as a foreigner in Japan, because I think it aptly describes the attitude that many of us are prone to adopting when we forget that we're not as awesome as Japan can make us feel.

Also, I found the PERFECT picture for this. BOOM!

Definition:
自分の力量をわきまえず、仲間うちで威張ること。知識も力もないのに尊大にふるまうことのたとえ。
Translations:
1. Getting a big head about being a big fish in a small pond, while forgetting that the world is mostly ocean.
2. Using your strength to be the boss of your microcosm, in a way that fails to acknowledge your real worth in the macrocosm. (What's your worth in the macrocosm NOW, fish?)
3. Act with reckless arrogance.

自大, using the kanji for "oneself" and "big" are apparent enough. 夜郎, rather than being ateji for 野郎、is actually the name of a very tiny independent country that we call Yelang in what is now China. The king of Yelang, upon receiving an emissary from the Han Dynasty (yeah, THAT Han Dynasty) displayed remarkably poor judgement (as well of a lack of knowledge about what the Han Dynasty was) and made some unfortunate boasts.

I don't know how accurate this story is, as the accounts of said king also include a Taketori Monogatari-esque birth...

Use 夜郎自大 with になる。Or you can say of someone or something: 夜郎自類である。

例文：
この学校の六年生の態度はやばいですね。行動を正してやる先輩もないし、夜郎自大になってしまいました。来年は中学生になることを知識してないみたい。
This school's 6th graders are rough, huh? With no older students to keep them in line, they've gotten recklessly arrogant. It's like they've forgotten that they're gonna be middle school first years in just a year.