In a large bowl, combine buttermilk, hot sauce, salt, and pepper. Whisk until well mixed. Add chicken thighs, ensuring they are fully submerged. Cover and refrigerate for at least 2 hours, preferably overnight.

In a shallow dish, mix together flour, paprika, cayenne pepper, garlic powder, onion powder, salt, and pepper. Stir until evenly combined.

Remove chicken from the marinade, allowing excess buttermilk to drip off. Dredge each piece in the flour mixture, pressing lightly to ensure an even coating. Shake off excess flour.

In a large skillet, heat enough vegetable oil to cover the bottom of the pan, about 1/2 inch deep, over medium-high heat until it reaches 350°F (175°C).

Carefully add the coated chicken thighs to the hot oil, frying for about 10-12 minutes on each side, or until golden brown and cooked through (internal temperature should reach 165°F or 75°C). Remove from oil and let drain on paper towels.

In a small bowl, combine vegetable oil, cayenne pepper, brown sugar, paprika, garlic powder, onion powder, and salt. Mix until well combined.

Brush the hot oil mixture generously over each piece of fried chicken, coating every side. Let the chicken rest for a few minutes before serving.