as cool as a cucumber (尤指意料之外地)非常冷静，泰然自若

【例句】
Though it was his first great venture, he was now as cool as a cucumber.
虽然这是他第一次的大冒险事业，但是他却非常冷静。

Her parents are always as cool as a cucumber,but she is bad-tempered.
她的父母一直很冷静，但是她脾气暴躁。