The weight of 无耻 (wúchǐ) is deeply rooted in Chinese cultural values, particularly the concept of 面子 (miànzi), or “face,” which represents a person's reputation, dignity, and social standing. To be 无耻 is to act in a way that completely disregards one's own 面子 and the social harmony it maintains. In traditional Confucian thought, a sense of shame (耻) was considered one of the cornerstones of a moral person. Mencius, a famous Confucian philosopher, stated that “a sense of shame is the beginning of righteousness” (羞恶之心，义之端也). Therefore, to be 无耻 (without shame) is to be seen as uncivilized, unrighteous, and outside the bounds of acceptable human behavior. Comparison to “Shameless”: While “shameless” is the closest English equivalent, it doesn't always carry the same heavy, moralistic condemnation as 无耻. In English, you can say “a shameless plug for my new book” or “she's a shameless flirt” with a neutral or even playful connotation. 无耻, however, is almost never playful. It is a direct and serious attack on a person's fundamental character. Using it in a lighthearted context where you might use “shameless” in English would be a significant cultural and linguistic mistake.
无耻 is a potent word used in situations involving serious moral transgressions. It's common in:
Because it is so strong, it is rarely used in polite or professional settings unless the goal is to create a major confrontation. Among very close friends, it might be used hyperbolically, but this is an exception.
In English, “shameless” can be neutral or even positive (e.g., “shameless self-promotion”). 无耻 is never positive. It is a 100% negative condemnation.
These two are very similar. 无耻 is slightly more formal and literary, while 不要脸 (bù yào liǎn) (lit: “don't want face”) is more colloquial and direct. Both are very strong insults.