keep your shirt/pants on，字面意思是让“衣服、裤子”都穿在身上，实际是劝你不要生气，保持冷静，别发火，要镇定。

【例句】
You need to keep your hair on, we will solve the problem together.
你需要冷静，我们会一起解决这个问题的。

Keep your hair on, Mum. You can hardly see the damage.
妈妈，保持冷静。你几乎看不到损坏。