Begin by preparing the shrimp. In a medium-sized bowl, combine the peeled and deveined shrimp with the buttermilk. Allow the mixture to sit for 10 minutes, which will help tenderize the shrimp.
While the shrimp is marinating, prepare the Bang Bang Sauce. In a small bowl, mix together the Japanese mayonnaise, Thai Sweet Chili sauce, and sriracha. Adjust the amount of sriracha based on your desired spice level. Set the sauce aside.
Prepare the dredging mixture by whisking together the cornstarch, salt, garlic powder, and black pepper in a shallow bowl or on a baking sheet.
Coat each shrimp thoroughly in the cornstarch mixture, ensuring an even layer on both sides.
In a large skillet or heavy-bottom pan, heat the vegetable oil over medium heat until it reaches 350 degrees F, or use a digital instant-read thermometer to check the temperature.
Fry the shrimp in batches, being careful not to overcrowd the pan. Cook the shrimp for about 1.5 minutes on each side until they are golden brown and crispy. Avoid overcooking the shrimp to maintain their tenderness.
Once cooked, transfer the shrimp to a wire rack or a plate lined with paper towels to drain any excess oil.
Place the crispy shrimp in a large bowl and pour the prepared Bang Bang Sauce over them. Gently toss the shrimp to ensure they are evenly coated with the sauce.
Garnish the shrimp with finely chopped green onions and serve immediately. Enjoy your Bang Bang Shrimp!