我不同意。

I don't agree.

我认为这个主意并不怎么样。

I don't think much of the idea.

我反对。

Objection.

这主意不好。

Bad idea.

这是个幼稚的想法。

That's a naive idea.

这样不好。

No good.

不，我想不是这样。

No,I don't think so.

这行不通的。

It won't work.

你疯了吗?

Are you crazy?

你一定是开玩笑吧。

You must be kiding.

这太荒谬了。

That's ridiculous.

简直是一派胡言。

That's sheer nonsense.