Pardon my French
粗俗语
It's a light hearted attempt at apologizing, usually used around people you know well but don't want to risk offending with bad language.
不是一个很走心的道歉，通常是你对你很熟悉的人，然后不想冒险直接说一些不好的话。就可以加上这个表达。

Going Dutch
AA 付账

Fly on the wall
偷听讲话的人
I wish I could be a fly on the wall in that situation!
我真想偷听，听听是啥情况。

A perfect storm
一场完美的风暴 （各种不幸的小事一起发生了）
The football match was cancelled due to a perfect storm of events, the bus was late, the referee couldn't make it and it started to snow too!
这个足球赛取消了，英文各种不幸的事情，车晚了，裁判员到不了，还下雪了！

At the drop of a hat
毫不迟疑的
He used to be very shy, going red at the drop of a hat.
他曾经很害羞，动不动就脸红。

An arm and a leg
很贵
Living in London costs an arm and a leg.
居住在伦敦的小费太高了。