Uncharacteristic (adjective)

1. Not typical of or in keeping with a person or thing's character or nature.
2. Not normal or usual for a particular person, situation, or thing.

Origin:

From un- ("not") + characteristic, from latin character ("mark, sign, characteristi.c")

Examples:

1. He was uncharacteristicly quiet during the meeting.
2. Her uncharacteristic outburst surprised everyone.
3. It was uncharacteristic of him to be so irresponsible.
4. He had an uncharacteristic lack of confidence.
5. It was uncharacteristic for her to be so indecisive.