play it cool

US /pleɪ ɪt kuːl/
UK /pleɪ ɪt kuːl/
"play it cool" picture
1.

冷静を装う, クールに振る舞う

to act in a calm, unemotional way so that people think you are not anxious or excited

:
When she saw her ex-boyfriend, she tried to play it cool.
元彼に会ったとき、彼女は冷静を装おうとした。
Just play it cool and don't show them you're nervous.
ただ冷静を装って、緊張していることを彼らに見せないで。