Talk Through One's Hat(make foolish statements)
We were discussing ethnic traditions and customs with Fred the other day, and he showed just how little he knew about other cultures.
What do you mean?
Well, he said that as far as he could tell, there wasn't much difference in behavior and temperament between the English and the Hispanics.
It's plain to see that he was talking through his hat!
True, but Fred thinks he's an authority on everything. It was difficult to convince him that he was talking ignorantly.
He's got a reputation for making foolish, inaccurate statements.
inaccurate = 不正確な
have a reputation for 〜 = 〜 であるとの評判だ