talk through one's hat

Attested from the late 19th century in the United States in the sense of “bluff”; the sense “speak without authority or knowledge” developed later. Although some people speculate a connection to a former requirement that British Members of Parliament wear hats, the connection is implausible.

• ""Mr. Pride said to me a moment ago that they spoke better English in Boston than any other place in the world." "Did he, though, Lady Lawless? That's good. Well, I guess he was only talking through his hat.""
• "No, sir, she yust standing pat, / And vonce more she tal her father, / “Yu ban talking tru yure hat!”"
• "He's conceited and opinionative and argues all the time, even when he knows perfectly well that he's talking through his hat."

• talk through one's ass

• nonsense
• BS