"任性" (ren xing) comes from a real story in 2014. There was an old man spending 1760 RMB to buy some kind of male health care product. Then he received a phone call from a stranger claiming that he has to buy other products to assist the health care product he has bought to get effect. The old man believed what the stranger said and got cheated with 5500 RMB. He realized he was taken in after he gave the fraud 70 thousand Yuan. But it didn’t end. The old man still sent money to the fraud because he just wanted to know how much money the fraud can cheat from him. Finally, he was cheated with more than fifty million.
When this event was exposed, netizens all claimed that the old man was "任性" (ren xing) because had much money. Suddenly, this words are prevalent through the online world. Meanwhile, "任性" (ren xing) is used for joke.