shoot oneself in the foot

By lying about his qualifications, he shot himself in the foot during the job interview.

彼は資格について嘘をついたが、面接でかえって不利になった。

She shot herself in the foot by arriving late to the important meeting.

彼女は重要な会議に遅刻したことで、かえって自分に不利な結果を招いた。