Lose your cool
Definition 1 of 1
Pro Tip 1/3Emotional Intensity
Used when emotions are so strong that they're hard to control, indicating a loss of composure. 
During the intense debate, he lost his cool and shouted.
Pro Tip 2/3Informal Setting
Mainly used in casual conversations, not in formal situations like business meetings. 
At the family dinner, I lost my cool over a silly joke.
Pro Tip 3/3Negative Connotation
Often viewed negatively, as it implies a lack of self-control or professionalism. 
The coach lost his cool with the referee and was ejected from the game.