too cool for school

cool cat

A person who performs or appreciates jazz, especially one whose style of speech and movement is relaxed and rhythmic.

cool head

A calm, focused demeanor and mindset; a person having such characteristics.

cool one's heels

To wait, especially impatiently or restlessly.

cool one's jets

To become less excited, intense, or active; to exercise self-restraint.

ice cool

calm and composed in a difficult situation.

keep a cool head

To keep one's cool; to stay calm.

keep one's cool

To remain composed, calm, and even-tempered, especially in a provocative situation.

lose one's cool

To become upset or disconcerted; to lose one's temper.