Someone who is very formal, pompous, or old-fashioned. I had heard he was a bit of a stuffed shirt, but he was very pleasant when I met him, and not pretentious at all.
An overly formal or pompous person, as in She's such a stuffed shirt that I'm surprised you'd invite her to a barbecue. This expression alludes to a shirt filled with paper (instead of a real person). [c. 1900]