keep your hair on 保持冷静；别发脾气；别生气

【例句】
Keep your shirt on! We’ve got plenty of time to get to the airport.
保持冷静，我们有足够的时间到达机场。

Keep your hair on. No one has done anything wrong, so there's nothing to get agitated about.
冷静点，没有人做错事，所以没有什么可焦虑的。