Without hesitation or compunction; calmly or unbothered (often implying doing something thoughtless or rude without concern).
彼は平気で嘘をつく。
He lies without remorse.
平気で人の写真をSNSに無断で投稿するのはよくない。
Posting someone's photo on social media without permission, as if it's no problem, is not good.
彼女はやけどをしても平気で働き続けた。
Even after getting burned, she continued to work as if nothing had happened.
平気で遅刻するクセを直した方がいい。
You should fix the habit of being casually late.