There are many synonyms for the phrase "loses cool" that can be used to describe someone who has become angry or frustrated. Some common synonyms include "gets heated," "loses their temper," "flies off the handle," "blows up," "gets agitated," "becomes irate," "loses their composure," "gets worked up," and "flares up." These synonyms all convey a similar sense of someone becoming overwhelmed with emotion and struggling to maintain their composure. Whether due to frustration, anger, or stress, the experience of losing one's cool can be a difficult and unpleasant one, which is why it's important to find effective ways to manage our emotions and cope with challenging situations.