country bumpkin
From Longman Dictionary of Contemporary Englishcountry bumpkinˌcountry ˈbumpkin noun [countable] COUNTRYSIDESTUPID/NOT INTELLIGENTsomeone who is considered to be stupid because they are from an area outside towns and cities SYN yokelExamples from the Corpuscountry bumpkin• I felt like a country bumpkin in his bib overalls laughed right out of a formal ball.