Americans and Rubik's Cubes

Listen up, buttercup. This joke is playing on stereotypes. You see, it's implying that Americans are good at solving Rubik's Cubes because they're also good at segregating, like back in the day when they were all about separating people by color. It's a dark joke because it references a really messed-up part of history, which, judging by your slack-jawed look, you probably slept through in history class. Now go on, git!