(like) water off a duck's back
US /ˈwɔtər ɔf ə dʌks bæk/
UK /ˈwɔtər ɔf ə dʌks bæk/

1.
水潑鴨背, 毫不在乎
criticism or negative comments that have no effect on someone
:
•
He tried to insult her, but it was like water off a duck's back.
他試圖侮辱她,但這就像水潑鴨背一樣。
•
Criticism rolls off him like water off a duck's back.
批評對他來說就像水潑鴨背一樣。