I don't get this joke from Modern Family (City mouse/country mice) Cam: Mitchell is a snob. Mitchell: No, I'm just discerning. Cam: Official slogan for snobs. When we first met, he wouldn't even look at me because I was a hick from the farm in Missouri, and he's a big **city mouse**. Mitchell: (snorts) Who says city mouse? Cam: **Country mice.** I don't get this city mouse / country mice joke. I know the meaning of every vocabulary here but I guess there's more to it cause I just don't get this conversation when it's taken literally. What's supposed to be funny in this context? Is "city mouse" or similar phrase of this sort a common joke in English? Thanks in advance!