keep/lose your cool
keep your cool
COMMON If you keep your cool, you control your temper and stay calm in a difficult situation. Hilde's one of those born managers — keeps her cool in a crisis. I knew I had to keep my cool, but it was hard.
lose your cool
COMMON If you lose your cool, you suddenly get angry and behave in a bad-tempered or uncontrolled way. At this point, I lost my cool and shouted `for goodness sake, stop!' `Why don't you sit down and have a drink?' — `I don't want a drink,' Anne replied, losing her cool.