stuffed shirt
From Longman Dictionary of Contemporary Englishstuffed shirtˌstuffed ˈshirt noun [countable] informal SERIOUS PERSONsomeone who behaves in a very formal way and thinks that they are importantExamples from the Corpusstuffed shirt• Marcus was a true intellectual stuffed shirt.• Modigliani clearly felt no empathy towards the stuffed shirt towering above his wife.