1. Stanley is a bit of a stuffed shirt. He’s arrogant and pompous and he tries to make everyone else think he’s so important.
2. We hate going to those business conventions. It’s just a bunch of stuffed shirts, sitting around trying to impress each other.

Compare to: old fuddy-duddy. Describing someone as a stuffed shirt is clearly disparaging, whereas old fuddy-duddy describes someone who is a harmlessly and often humorously old-fashioned person. The expression stuffed shirt is always used to describe a man, never a woman.