I see nothing trollish or racist about your question, and I'll answer directly. When blacks were doing slave labor in the cottonfields, they were fed watermelon on break. I'm not sure if black people actually like watermelon, but that is probably what started that stereotype. As for fried chicken, it's because of the diet slaves ate when they were laboring in the kitchen. It consisted of cajun and creole flavors mixed with a lot of chicken. Over centuries of passing down recipes and tastes to newer families, it's bound to still be popular to black families. It's basically ethnic African American food.