Definition & Meaning of "be full of shit"

What is the origin of the idiom "be full of shit" and when to use it?

The origin of the expression "full of shit" is unclear, but it is believed to have emerged as a colloquialism in the mid-20th century. The phrase is used informally to convey a sense of disbelief, skepticism, or disdain towards someone's statements or deeds. The phrase is often employed in casual conversations or informal settings to express frustration, disbelief, or to challenge the authenticity of someone's words or actions.