Keep Your Shirt On
Meaning
Calm down, be patient.
Example
Just keep your shirt on, dinner is almost ready.
Origin
Before modern manufacturing techniques, shirts, and all clothes for that matter, required a lot of labor to make. They were more expensive than they are today. Someone thinking of starting a fight might take off his shirt to prevent damage. Telling someone to keep his shirt on was equivalent to telling him I don’t want to fight.
