ants in one's pants (裤子里的蚂蚁)——表达就是“坐立不安”的含义了

【例句】 　
I am so nervous like ants in my pants. 　　
我就像热锅上的蚂蚁一样坐立不安。

Tom has ants in his pants for tomorrow's final exam.
Tom为明天的期末考试而紧张不安。