FDR: American Badass!

Am willing to bet not one person of million who saw this movie has noted the reference to "World War I" during a scene that takes place in 1931. Since WWII did not begin until 8 years later, how did they know The Great War was "World War I"? The movie itself I thought was very funny, and enjoyed it. It's obligatory now that every third word has to be f this and f that, in order to accommodate the teenagers. Only thing is, for this moving, the teenagers likely would not be interested anyhow, never having even heard of President Roosevelt. I spoke with a young woman, "history major" in her high school senior class, and she had no idea what was Pearl Harbor, that it was attacked, etc. FDR...who's he?