鲍鱼之肆 Fish Market
Explanation
鲍鱼之肆指的是卖咸鱼的店铺，比喻坏人聚集的地方，环境恶劣。久处其中，难免受到影响，就像长期闻到咸鱼的臭味，也会变得臭一样。
"Bào yú zhī sì" refers to a shop selling salted fish, it is a metaphor for a place where bad people gather and the environment is bad. Staying there for a long time, it is inevitable to be affected, just like the long-term smell of salted fish, will also become smelly.
Origin Story
话说东汉时期，有个叫刘向的人，他非常注重品德修养。一天，他看到一个朋友整天和一些品行不端的人在一起，就劝诫他说："和坏人在一起，就像进入卖咸鱼的店铺一样，时间长了，你也会闻不到臭味了，不知不觉中变得和他们一样。"朋友听后，深感惭愧，从此远离那些坏人，改过自新。
In the Eastern Han Dynasty, there was a man named Liu Xiang, who attached great importance to moral cultivation. One day, he saw a friend hanging around with some immoral people all day long, so he advised him, "Associating with bad people is like entering a shop selling salted fish, after a long time, you will not smell the stench, and you will unconsciously become like them." After listening to his words, the friend felt deeply ashamed and stayed away from those bad people ever since.
Usage
用作宾语；比喻坏人聚集的地方
Used as an object; a metaphor for a place where bad people gather
Examples
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他整天和那些不三不四的人混在一起，简直就是身处鲍鱼之肆。
ta zhengtian he na xie busanbushi de ren hun zai yiqi, ganzhi shi shen chu baoyu zhi si
He spends all day with those disreputable people, it's like being in a fish market.
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这样的环境，简直就是鲍鱼之肆，令人难以忍受。
zheyange huanjing, ganzhi shi baoyu zhi si, ling ren nanyi ren shou
Such an environment is simply a den of iniquity, unbearable.