In a large bowl, combine shrimp and buttermilk. In a separate bowl, combine the cornstarch, garlic powder, salt, and, black pepper. Remove the shrimp from the buttermilk, drain the excess liquid and coat in the cornstarch mixture.
To make the bang bang sauce, combine the mayonnaise, Thai sweet chili sauce, Sriracha and a pinch of salt in a small bowl. Set aside or refrigerate until ready to use.
Heat 2 to 3 inches of oil in a heavy bottomed pan, over medium heat (350°F to 375°F.). Add the shrimp and fry until lightly brown, 1 to 2 minutes per side.
Remove from the oil and place on a cooling rack to drain. Coat the crispy shrimp with the sauce. Serve immediately over a bed of shredded lettuce and garnish with garnishes of choice. Enjoy!
