The original meaning of the word mad dog refers to mad dog, which comes from "mad dog and stubborn dog" in Shuowen. The extension refers to "people's insanity" and "madness", such as "crazy man bends over backwards" in the poem Qi Feng Dongming.
In the history of China, "madness" is often used as a cover for speaking freely. When a minister wants to criticize the emperor radically, he will call himself a "crazy fool". For example, Wei Zhi told Emperor Taizong that "a madman's words let a saint choose his own way". Similarly, that spontaneous and irregular attitude towards life is also called or calls itself "crazy".