They invented some lamebrain scheme to get rich quick.

为发横财，他们想出了个蠢办法。

There is no need to accuse him of being a lamebrain.

没有必要指责人家笨。

The next time your friend does not get one of your jokes, there is no need to accuse him of being a lamebrain.

下次你的朋友听不懂你讲的笑话时，没有必要笑人家笨。