1. In a large bowl, combine buttermilk, salt, black pepper, paprika, garlic powder, and onion powder.
2. Add chicken thighs to the buttermilk mixture and marinate for at least 2 hours or overnight in the refrigerator.
3. In another bowl, add flour, salt, and pepper. Mix well.
4. Heat the vegetable oil in a deep fryer or large pot to 350°F (175°C).
5. Remove chicken from the buttermilk mixture, letting excess drip off. Dredge in the flour mixture, ensuring an even coat.
6. Fry the chicken in batches until golden brown and cooked through, about 10-12 minutes per piece.
7. Remove chicken from oil and drain on paper towels. Serve hot.