Cook bacon in a skillet over medium heat, turning occasionally until browned and crisp. Drain bacon on paper towels, reserving fat in skillet. Finely chop bacon.Add onion and okra to skillet with bacon fat and cook, stirring until vegetables begin to soften, about 3 to 5 minutes. Remove from heat and add chopped bacon.In a mixing bowl, combine egg, buttermilk, cornmeal, brown sugar, and cayenne. Whisk until smooth. Stir in onion, okra, and bacon mixture.Wipe skillet clean, add vegetable oil, and place over medium heat. Add small, rounded tablespoons of batter to skillet, turning once, until golden brown, 2 to 3 minutes per side. Transfer fritters to paper towels to drain. Serve immediately.