In Chinese culture, both traditionally and today, courage (勇敢, yǒnggǎn) and a sense of righteousness or honor (义气, yìqì) are highly esteemed virtues. A person is expected to show bravery not just for personal gain, but to protect their family, stand by their friends, and uphold their responsibilities. Therefore, being labeled a “懦夫” is a profound insult. It's not just a comment on one's fear; it's a condemnation of one's entire character. It implies a person has lost “face” (面子, miànzi) and has failed in their social and moral duties. A useful comparison is the Western concept of a “coward” versus “懦夫”. While both are negative, “懦夫” is often more deeply connected to a betrayal of social bonds. A Western “coward” might be someone who simply saves their own skin. A “懦夫” is often someone who, through their cowardice, lets down their friends, family, or community, thereby violating the principles of “义气” (yìqì) - the code of honor and loyalty between people.
“懦夫” is a harsh and direct insult. It is almost always used in a negative and confrontational context. You would not use this word lightly.