In a large mixing bowl, combine buttermilk, salt, black pepper, onion powder, and garlic powder. Add the shrimp, ensuring each piece is well-coated in the marinade, and let it sit for 15 minutes.

While the shrimp is marinating, place corn starch in a shallow bowl. After 15 minutes, remove the shrimp from the marinade, letting the excess buttermilk drip off. Dredge each shrimp in the corn starch and set aside.

Heat peanut or canola oil in a skillet over medium-high heat until it reaches about 350°F (180°C). Carefully add the coated shrimp to the hot oil in batches and fry for 2-3 minutes per side until golden brown and crispy.

In a medium bowl, combine mayonnaise, Thai sweet chili sauce, and Sriracha, adjusting the amount of Sriracha to reach your desired level of spiciness. Mix well until the sauce is smooth and creamy.

Warm your tortillas in a dry skillet over medium heat for about 30 seconds per side, or until pliable. Begin layering by adding a base of shredded cabbage, followed by diced tomatoes, a generous portion of crispy shrimp, and a drizzle of the Bang Bang sauce. Top with freshly chopped cilantro.