country bumpkin

Someone from a rural area who is therefore not versed in city life or its social norms. Cousin Celia is such a country bumpkin. Last time, she took her shoes off in the middle of a restaurant! Can you dress a little nicer? You look like a country bumpkin in those overalls! I can't believe there are country bumpkins like you who have never been to a big city.

a country ˈbumpkin/ˈcousin

(informal, usually disapproving) a person from the countryside who is not used to towns or cities and seems stupid: He felt a real country bumpkin, sitting in that expensive restaurant, not knowing which cutlery to use.