keep one’s shirt on 不慌张，不发脾气，保持镇静，别着急，耐心点

【例句】
He was beginning to holler, so I told him to keep his shirt on.
他大声叫喊起来了，所以我才叫他保持镇静。

They won't be here for another hour. Keep your shirt on.
他们还有一小时才到，别着急。