out of character; unlike one
Used when someone does something that doesn't match their usual personality or behavior. Often followed by a verb phrase describing the unexpected action.
See also: 柄にもない (がらにもない)
He started talking with a serious face, which was out of character for him.
I got nervous, which is unlike me.
Alternate kanji spelling using 無く instead of なく.
From 柄 (がら, 'one's character or nature') + に (particle) + も (even) + なく (adverbial form of ない, 'not'). Literally 'not even in one's character'.