godan verb (-ru), intransitive verb
act cool; play it cool
Colloquial verb meaning to behave in a cool, detached, or nonchalant manner, often with a slightly affected or self-conscious nuance.
See also: ぶる
彼はいつもクールぶってるけど、本当は緊張してるんだよ。
He always acts cool, but he's actually nervous.
You don't have to act so cool, you know.