A four-character idiom meaning utter indifference — to let remarks go in one ear and out the other.
先生の注意も、彼には馬耳東風だった。
The teacher's warning just went in one ear and out the other for him.
上司の忠告が馬耳東風になっている部下をどう指導するかが課題だ。
How to deal with subordinates who ignore their boss's advice is the problem.
いくら苦情を出しても、役所は馬耳東風のように対応した。
No matter how many complaints were filed, the office responded as if they didn't care.