as silly as a goose 蠢极了；非常笨

【例句】
Jane did such a thing, she is really as silly as a goose.
简竟然干出这种事，她实在是太蠢了。

Since he is as silly as a goose, he will not get a promotion.
既然他如此的不开窍，他肯定得不到提升的。