You are so stupid.
真笨───How stupid;你───you
How stupid you are!───你这人好浑啊！
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。
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。
'Well, Father', said Nasreddin, , this time I thought that I would do just what you told me, to show you how stupid your orders always are.───“哦，爸爸，”纳斯瑞丁说：“这一次我想我偏要照你说的做，让你看看你的指挥一向是多么愚蠢。”
I don't remember how much I love to cry and why on earth am I on this earth. All I know is how stupid and foolish I am.───我从来都不记得究竟多么爱哭。我也不知道自己究竟为何来到这个世界上。我知道自己好笨好傻。
How stupid of him to ask such a question!───他问这样的问题，多蠢！
She really opened my eyes to how stupid I'd been.
How stupid to fall on your face.
Now one might say: more fool them, how stupid to build their Alpine villages in the paths of potential avalanches.
It makes me cringe when I think how stupid I was.
It struck me how stupid it is.