What is the origin of the idiom "shit hit the fan" and when to use it?

The idiom "shit hit the fan" is a originated in the mid-20th century. It is a vivid and informal way of describing a situation where chaos, trouble, or a significant problem suddenly arises or escalates. The idiom is used to imply that the situation has reached a critical point where the negative consequences become apparent and unavoidable. The phrase uses a vulgar term for emphasis and to convey a sense of shock or intensity.