noun
forgetful person
A mildly teasing or affectionate term for someone who often forgets things; common in casual speech and children's language.
うちの子は忘れん坊で、毎日何か学校に忘れてくる。
My kid is so forgetful; every day they leave something at school.
また鍵を忘れたの？本当
You forgot your keys again? You're such a forgetful person.