lose one's cool

Example: “The usually calm coach lost his cool at the referee.”

Origin: Builds on "cool" as a description of calm, composed self-control, a figurative use already established by the 1920s, well before it was applied to jazz. Miles Davis's 1949–50 recordings, later released as the 1957 album Birth of the Cool, gave the word a specific cultural charge in the mid-20th century, contrasting his restrained, understated style against the louder, more emotionally charged "hot jazz" that had dominated earlier decades. "Lose one's cool," for losing that same composure and self-control, follows in the mid-1960s, with the earliest clearly documented use from a 1964 newspaper article — a natural next step once "cool" itself had become firmly established slang for exactly the calm, unflustered state one could lose.