scatterbrain
noun [ C ] informal uk/ˈskæt.ə.breɪn/ us/ˈskæt̬.ɚ.breɪn/
健忘的人；轻率的人
a person who forgets things easily or does not think seriously about things
I'm such a scatterbrain - I'm always leaving my bag behind. 我真没脑子——我老是忘了自己的包。