Entymology/usage: To call someone a "stuffed shirt" is of course, derogetory. The shirt is given more credit than the person wearing (or stuffing) it by the person wielding this insult. It is used widely in describing politicians or a loud-mouthed employer.
Jordan Gilbert is a stuffed shirt.
A habitual bore or fuddy duddy.
And the public praise you win;
There's your picture in the Press,
Pouchy eyes and triple chin.
Wealth,--of it you fairly stink;
Health,--what does your Doctor think?
- From 'To A Stuffed Shirt' by Robert Service.