What is the origin of the idiom "stuffed shirt" and when to use it?

The idiom "stuffed shirt" originated in the early 20th century and refers to a person who acts really serious, formal, and full of themselves. It's like picturing a person wearing a shirt that's stuffed with padding, making them seem stiff and inflexible. This phrase is used to talk about people who are too proper, always following strict rules, and thinking they're more important than they really are. It's a way to make fun of them and show that they don't have much personality or the ability to be easygoing.