In a medium bowl, combine the medium to large shrimp with buttermilk, salt, garlic powder, onion powder, and black pepper. Stir well to ensure the shrimp are fully coated. Let the mixture marinate for 10 minutes while you prepare your workspace for frying.

While the shrimp are marinating, set up your dredging station. Place cornstarch in a shallow dish. Remove the shrimp from the marinade, shaking off excess buttermilk before dredging them in cornstarch.

In a large pot, pour in enough oil to reach about 1.5 inches deep. Heat the oil over medium-high until it reaches 350°F.

Once the oil is hot, carefully drop the breaded shrimp into the pot in batches, frying each for about 2 minutes or until golden brown and crispy. Transfer cooked shrimp to a paper towel-lined plate.

In a large bowl, combine mayonnaise, Thai sweet chili sauce, and Sriracha. Stir until smooth. Adjust the Sriracha to your taste.

Add hot shrimp to the bowl with the bang bang sauce and toss to coat evenly.