What is the specific meaning of the idiom "rough skin"?

1, describing rough skin and fat. It means people are rough.

2. antonym: the skin is fine and tender, which is an idiom in China. The pinyin is xì pí nè nê rê u, which means that the skin is well maintained, delicate and fair. From the fourteenth story of Zen Buddhism by Taoist Qingxi in the Ming Dynasty: "An old friend has to retire quickly. These monsters often say that the young ones are tender and hungry quickly, but they are not as hard as the old ones. Some bite and chew, and they just want to eat the old ones. "