i think it means "shut your mouth up" and i suggest you reply immediately with "you too" to make an equal. it is just like "pain in the neck" (which really means "pain in the ass").[/COLOR]
that's the phrase people say when they swear. Generally, people need to learn the way of saying such a thing properly, they might say something else instead. But, it depends. It has to refer to the situation, and sometimes people's facial expression, etc.