Handle something well
处理得很好，表现得很冷静

Yeah, he was a jerk, but you handled that well.
没错，他是个混蛋，但你处理得很好。

She handled the news well. I thought she was going to freak out.
她听到新闻后表现得很冷静。我还以为她会崩溃呢。

You handled that well. Good job!
你处理得很好，很棒！

Lose one's cool
失去风度，不镇定，不理智

You didn’t lose your cool and still showed him respect, even though you didn’t have to.
你没有失去风度，虽然不必，但依然给予了他尊重。

He lost his cool and started yelling at everyone.
他失去了风度，开始朝大家大喊大叫。

I shouldn’t have lost my cool. I’m sorry for how I acted.
我不应该那么不理智。我为我的行为道歉。