(as|) cool as a cucumber

untroubled by hot temperature or physically difficult actions

He leaps up the six flights of stairs and arrives at the top as cool as a cucumber.

used to describe someone who is not worried at all in challenging or stressful situations

The exact origin of the idiom "cool as a cucumber" is uncertain, but it has been in use since the late 17th century. It likely arose from the association of cucumbers with a cool temperature and the idea of maintaining composure. The phrase is used to describe someone who stays calm and collected in difficult situations. It is used in various contexts to describe individuals who remain calm and composed in challenging or stressful situations. It can be applied in personal conversations, discussions about someone's demeanor, or even in professional settings.

Despite the intense competition, he kept his cool as a cucumber and delivered a flawless performance.
During the job interview, she answered every question confidently and without hesitation, appearing as cool as a cucumber.
Even though the situation was chaotic, she remained cool as a cucumber, calmly directing everyone and finding a solution.
The goalkeeper remained cool as a cucumber, saving every penalty shot with ease.
I was nervous, but she was cool as a cucumber, guiding me through the process.