https://en.wikipedia.org/wiki/Watermelon_stereotype

After the American Civil War, in several areas of the South, formerly enslaved individuals grew watermelon on their own land as a cash crop to sell. Thus, for African Americans, watermelons were a symbol of liberation and self-reliance. However, for many in the majority white culture, watermelons embodied and threatened a loss of dominance. Southern White resentment against African Americans led to a politically potent cultural caricature, using the watermelon to disparage African Americans as childish and unclean, among other negative attributes

Fragile white people getting mad at their fellow poors instead of the rich assholes keeping them all in the dirt.