Narrator Nick Carraway has a great deal of fun with Gatsby's ignorance, hinting at the novel's satiric roots: Fitzgerald initially based his most famous novel on a Roman satire about an upstart slave named Trimalchio who becomes rich and gives lavish feasts. In fact, to his editor's great alarm, Fitzgerald wanted to call the book Trimalchio, a reference most people would not understand.
Vestiges of this satire remain in chapter IV, as Nick and Gatsby drive to New York in Gatsby's "gorgeous car." Nick asks Gatsby what part of the midwest he comes from and Gatsby answers San Francisco. Gatsby goes on to tell Nick of living "in all the capitals of Europe--Paris, Venice, Rome--collecting jewels, chiefly rubies, hunting big game ..." As Nick drily notes, he has to "restrain ... laughter," for people don't hunt big game in European cities. Nick, with derision, imagines Gatsby as a "turbaned" character chasing a tiger through Paris's Bois de Boulogne. Gatsby, we see, doesn't know Paris from India.
Gatsby shows his ignorance of upper-class ways by calling people "old sport," a British affectation that drives Tom, in particular, crazy. We see too, that though Gatsby has real books in his library (something Owl Eyes notes) he hasn't cut the pages, meaning he doesn't actually use the library as more than a prop to make him look like a cultured member of the learned class.