The characters combine literally to mean “clumsy mouth and awkward tongue.” This creates a powerful and visual image of the physical organs of speech not working properly, resulting in fumbled words and awkward expression.
The most important context for `笨口拙舌` is the Chinese cultural value of 谦虚 (qiānxū) - humility or modesty. In many Western cultures, it's common to project confidence before a speech, saying something like, “I'm excited to share my thoughts with you.” In contrast, a traditional Chinese approach is to lower expectations and show modesty. By saying you are `笨口拙舌`, you are managing expectations, showing respect for the audience, and framing any potential mistakes as a result of your own inadequacy rather than disrespect. This contrasts with the Western concept of being “tongue-tied.” A person is usually “tongue-tied” due to a specific, overwhelming emotion like shock, infatuation, or extreme nervousness. `笨口拙舌`, however, is often used proactively as a polite social formula, a way of “padding” one's introduction to appear humble. It's less about an emotional state and more about performing a social role. Using it signals that you are not arrogant and that you value the audience's time and opinion.