1. waiting in the wings

Wings原本是指剧院里演员等候上台的地方，字面意思是等待上台表演，如今引申为做好准备等待机遇的到来，翘首以待（to be ready to be used or employed）

例句：

They say Bob will be fired and I'm waiting in the wings to take over.

据说鲍勃将被辞掉，我坐等接任他的职位。

2. weak at the knees （通常指因看到或谈到非常喜欢的人或让人害怕、激动的事而）无法站稳，膝盖发软的，腿发软的

例句：

The very thought of jumping off the bridge made him go weak at the knees.

想到要跳下桥他吓得腿都软了。

The thought of kissing him made me go weak at the knees.

吻他的念头令我膝盖发软。