Marinate the Chicken: In a bowl, add the buttermilk, garlic powder, onion powder, salt, and pepper. Mix well. Add the chicken thighs, coat them in the marinade, cover, and refrigerate for at least 1 hour (or overnight for best results).
Prepare the Coating: In a shallow dish, mix together flour, cornstarch, paprika, cayenne pepper, salt, and pepper. Set aside.
Heat the Oil: In a deep skillet or frying pan, heat the vegetable oil over medium-high heat until it reaches 350°F (175°C).
Bread the Chicken: Remove the chicken from the marinade, allowing excess liquid to drip off. Dredge each chicken thigh in the flour mixture, pressing lightly to ensure an even coating.
Fry the Chicken: Carefully place the coated chicken thighs in the hot oil, working in batches if necessary. Fry for about 6-7 minutes on each side or until golden brown and cooked through (internal temperature should reach 165°F or 75°C).
Make the Sauce: In a small bowl, combine mayonnaise, sweet chili sauce, sriracha, and honey. Mix until smooth and well blended. Adjust heat level by adding more sriracha if desired.
Serve: Remove the chicken from the oil and place it on paper towels to drain excess oil. Drizzle the bang bang sauce over the chicken thighs, or serve it on the side for dipping.
Garnish: Sprinkle sliced green onions and sesame seeds over the chicken for added flavor and presentation.