Definition & Meaning of "watch {one's} [mouth]"

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

The idiom "watch one's mouth" originated from the idea of keeping a close eye on what one says or how one expresses oneself. It is often used to advise or warn someone to be more careful with their words and to avoid using offensive or disrespectful language, especially when they might be speaking inappropriately or insensitively. This phrase is typically used in informal conversations and carries the implication that the speaker should exercise self-control in their speech.