expression, i-adjective
not funny; no laughing matter; serious
Used when a situation is too serious or severe to be joked about. Often implies real danger, trouble, or offensiveness.
あの事故は洒落にならない。
That accident is no laughing matter.
冗談じゃ済まない、洒落にならない話だ。
It's not something to joke about; it's a serious matter.
Also means 'it's not a joke', but 洒落にならない emphasizes that the situation is too grave for humor, while 冗談じゃない can express anger or disbelief more directly.
From 洒落 (joke, pun) + にならない (is not becoming, is not acceptable). Literally 'it doesn't become a joke', i.e., the matter is too serious to be treated as a joke.