I could not undestand what he was sorry about, and I just said, "Bye!" After a moment of thinking, I realized how stupid I was.

我不明白他为什么道歉，就说：“再见！”经过片刻的思考，我意识到我是多么的愚蠢。

youdao

How stupid you are!

你这人好浑啊！

《新英汉大辞典》

How stupid you were. You should have known what he was driving at.

你真傻，他这点意思都听不出来。

《新英汉大辞典》

But, you see, nobody knew the secret of how stupid he really was.

VOA: special.2009.01.03

But,you see,nobody knew the secret of how stupid he really was.

VOA: special.2010.03.27

' And so,I wrote the song called 'Why Didn't I Think of That?'" "How incredibly stupid not to have thought of that myself.

VOA: standard.2009.11.25

Another ETF company is counting on investors not noticing how stupid this comparison is.

FORBES: A Call for Ethics in ETF Advertising

Look how stupid this Dutch tradition is, it probably this or looks like that.

FORBES: The Unbearable Whiteness of Piet-ing: Dutch Santa's Blackface Elves

Just how stupid can nominally intelligent people be about mortgage interest rates?

FORBES: Just How Stupid Can People Be About Mortgage Rates?