From Longman Dictionary of Contemporary Englishlose your coollose your coolANGRYFRIGHTENEDto stop being calm in an annoying or frightening situation Kenneth finally lost his cool with a photographer, and threatened to hit him. → cool
Examples from the Corpus
lose your cool• Kenneth finally lost his cool with a photographer this morning, and threatened to hit him.• Gable lost his cool with his pal Spencer Tracy who often tested the patience of his peers.• I should not have lost my cool and behaved in that manner.• He lost his cool and kicked out two stumps during a frustrating day when he beat the bat consistently.• Sam was a real gentleman who never lost his cool.• In this situation, it hardly ever helps if you start shouting or losing your cool.• Sometimes she lost her cool and I thought she stepped out of her role as therapist.• But she was not the only one who was losing her cool. 