cool as a cucumber

Cool as a cucumber is a phrase which is used to explain that someone is extremely calm and in control of their emotions. Cucumbers are cool in the literal sense in that they are a neutral vegetable, with a calming taste and a cool-like temperature. Figuratively, to be cool as a cucumber means to be a person who is often very simple and calm, and in control of your emotions without becoming moody or exaggerating your negative emotions.