What is the origin of the idiom "flap one's gums" and when to use it?

The origin of the phrase "flap one's gums" is not definitively known, but it likely stems from the visual imagery of someone's gums moving rapidly as they talk excessively or without purpose. The phrase has been in use since at least the early 20th century and has become a common expression in English to describe the act of talking a lot without saying anything meaningful. The emphasis on the movement of the gums in the phrase emphasizes the lack of substance or relevance in the person's speech. It's worth noting that the phrase is colloquial and informal in nature.