(Saru ni eboshi; “A courtier’s cap on a monkey”)
When the appearance of something is all dressed up, but doesn’t match its real content. Alternately, unfitting behavior. Like putting a fancy hat of the kind that used to be worn by aristocratic men in the imperial court… on a monkey. Like lipstick on a pig, or an expensive suit on an evil clown, but perhaps cuter.
This simple phrase begins with the noun 猿 (saru), “monkey,” and ends with the noun 烏帽子 (eboshi), which is the name of a style of hat worn by Japanese court officials back in the day, based on a design imported from the mainland. They’re joined by the particle に (ni), which applies the latter noun to the former. The causative form of a verb such as 被る (kaburu), “to wear (on one’s head),” is implied but elided.
There are several variants of this phrase, mostly replacing 烏帽子 with 冠 (kanmuri), “crown,” or the more generic 衣 (koromo), “clothing.”
This is a common style of eboshi, by the way:
(“Iyaa, itsumo kudaketa fun’iki ga tadayou ano hito ga anna katai iikata de hanasu nante, maru de saru ni eboshi da. Iwakan shika nai ne.”)
[“Naaah, they always have such a laid-back attitude that when they talk in a formal way it feels really inappropriate. It just makes me uneasy.”]