What he said was idiotic.

他的发言愚蠢透顶。

The audience asked a very idiotic question at the scene.

这个观众在现场问了一个很愚蠢的问题。

It was a completely idiotic decision.

这完全是一个白痴一样的决定。

I am chary of making too many idiotic mistakes.

我小心谨慎以免犯太多的愚蠢错误。

"Oh, there's no use in talking to him," said Alice desperately: "he's perfectly idiotic!"

“唉，跟他说话没用。”爱丽丝绝望地说，“他完全是个白痴！”

That's an idiotic reply though.

那是愚蠢的回答。

This is not only wrong but idiotic.

这不是唯一的但是最愚蠢的错误。

Say you are idiotic are raising your grades.

说你是脑残都是提高了你的档次。