“没种” is deeply rooted in cultural ideas about honor, courage, and masculinity (`男子气概 - nánzǐ qìgài`). In many situations, backing down from a challenge or showing fear can lead to a loss of face (`面子 - miànzi`). To call someone “没种” is to directly attack their character and social standing in this regard. A useful Western comparison is the phrase “to have no balls.” Both terms are vulgar, gendered (though they can be used toward anyone), and serve as a direct challenge rather than a simple observation. However, “没种” is arguably more mainstream in everyday confrontations in China than “no balls” is in the West. It's a go-to insult for questioning someone's backbone. This contrasts with a more neutral descriptive term like “timid” (`胆小 - dǎnxiǎo`). While “dǎnxiǎo” describes a state of being fearful, “没种” is an accusation of a fundamental character flaw. It implies that the person is inherently weak and lacks the essential quality of courage.
This term is exclusively informal and negative. Using it in a formal or professional setting would be a major social blunder.