表达“as cool as a cucumber 像黄瓜一样冷静”可以理解为“处变不惊、泰然自若”，即形容人在压力下显得极为冷静，毫不动容。单词 cool 在这里的意思并不是“清凉的”，而是指人“镇定、沉着的”样子。
Hearing the news, everyone in the room panicked except for Tracey - she looked as cool as a cucumber.
The exam is in less than an hour, but I'm as cool as a cucumber.
The actress was as cool as a cucumber after winning her Oscar. She looked poised and elegant as usual.