Think of something that is meant to fit you and does not. A jacket can be beautiful on the and wrong the moment you put it on, because the question was never whether it is nice — it is whether it goes with you. Now hand the same question to an action: this is a fine thing for someone to do, but does it go with you, in the position you hold?
可以想成一樣「本來該合你」的東西，偏偏不合。一件外套掛在架上很好看，一穿上身就不對了。因為問題從來不是它漂不漂亮，而是它配不配得上你這個人。接著把同一個問題交給一個行為：這件事本身也許沒什麼，但配不配得上你現在的身分？unbecoming 問的一直是這個「合不合」。
From the word’s history
Wiktionary gives un- plus becoming, and compares Middle English unbicomelich; it also notes the parsing unbecome plus -ing. Becoming as an adjective is the positive partner, saying a thing does suit you.
Wiktionary 記載它由 un- 加 becoming 構成，並指出中古英語有對應的 unbicomelich，也提到可以看成 unbecome 加 -ing。becoming 當形容詞時是它的正面搭檔，意思是「襯得上你」；加上 un- 就成了「配不上」。
Wiktionary, "unbecoming"
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