stuffed shirt

1. N-COUNT If you describe someone, especially someone with an important position, as a stuffed shirt, you mean that they are extremely formal and old-fashioned. (尤指身居要職的)一本正經的人; 古板守舊的人[非正式]

In a pinstriped suit he instantly looked like a stuffed shirt. 穿上一套細條紋西裝後，他馬上就顯得一本正經。