out of character
to be unlike one's usual character, to be inappropriate for one's character
Getting into an argument with the sales clerk was out of character for my father. He almost never argues about such things.

[TahlilGaran] English Idioms Dictionary ▲

out of character
adv. or adj. phr.
1. Not in agreement with a person's character or personality; not in the way that a person usually behaves or is expected to behave; not usual; unsuitable; uncharacteristic.
Mary is a nice girl. Her fit of temper was out of character.
2. Not in character; unsuitable for a part or character.
It isn't always out of character for a young actor to play an old man, if he is a good actor.
Antonym: IN CHARACTER.

[TahlilGaran] English Idioms Dictionary ▲