Inappropriateness is the ordinary noun for not being suitable or not being right in a particular situation. If inappropriacy is the slightly more academic twin, this is the one you will meet more often in everyday English, especially American English. We use it about comments, clothes, timing, and behaviour: the inappropriateness of phones at dinner, of a joke that went too far, of a gift that was too personal. Though actually it still names fit, not evil. A kind sentence can have inappropriateness if the moment is wrong. It is a little formal — in speech people often say “that was not appropriate” instead of naming the noun — but it is not rare, and students will see it in school rules and workplace writing.

不恰當、不得體（較常用的名詞說法）