What is one regional thing in your country that foreigners think represents your entire country?

I would say that for Mexico it would be Regional Mexican music. As a child born to two Mexican immigrants in the USA I can say most of the Mexican diaspora here listens to regional mexican music, but up until very recently (corridos tumbados) its only been a genre popular with rural working class people in Mexico. Hell, I would even say Mexicans living in the USA love regional Mexican music more than Mexicans.