当耳旁风 to treat something as if it were nothing
Explanation
比喻把别人的话当作耳边吹过的风一样，根本不放在心上，不予理睬。
It means to treat other people's words as wind passing by the ears, not taking them to heart, and ignoring them.
Origin Story
从前，有个年轻人名叫小明，他非常骄傲自负。一天，一位经验丰富的长者语重心长地劝诫他，要谦虚谨慎，认真听取别人的意见。小明却满不在乎，对长者的教诲充耳不闻，只顾自己玩乐。后来，他在一次重要的决策中因为轻敌冒进而遭受了巨大的损失。他这才后悔莫及，明白长者的话并非耳边风，而是宝贵的经验教训。
Once upon a time, there was a young man named Xiaoming who was very proud and self-confident. One day, an experienced elder earnestly advised him to be humble and cautious and to listen carefully to others' opinions. Xiaoming, however, was unconcerned and ignored the elder's teachings, preferring to play. Later, in an important decision, he suffered a great loss due to underestimation and recklessness. Only then did he regret it and understand that the elder's words were not just empty talk but valuable lessons.
Usage
用于形容对别人的话不放在心上，置之不理。
Used to describe someone ignoring other's words and not taking them seriously.
Examples
-
他总是对我的建议置之不理，简直是当耳边风。
tā zǒngshì duì wǒ de jiànyì zhì zhī bù lǐ, jiǎnzhí shì dāng ěr páng fēng.
He always ignores my suggestions; he simply treats them as if they were nothing.
-
领导的批评，他都当耳旁风，一点也不放在心上。
lǐngdǎo de pīpíng, tā dōu dāng ěr páng fēng, yīdiǎn yě bù fàng zài xīn shang.
He takes the boss's criticism as nothing serious, he doesn't take it to heart at all.
-
对于那些流言蜚语，他一向是当耳旁风，从不理会。
duìyú nàxiē liúyán fēiyǔ, tā yīxiàng shì dāng ěr páng fēng, cóng bù lǐhuì
He always ignores the gossip and never pays attention to them