Place shrimp in a bowl with buttermilk. Let marinate for 15–30 minutes for extra tenderness and flavor.
In a small bowl, whisk together mayonnaise, Thai sweet chili sauce, sriracha, and lime juice until smooth. Set aside.
In a shallow dish, mix cornstarch, garlic powder, onion powder, salt, and black pepper.
Remove shrimp from buttermilk, allowing excess to drip off. Dredge each shrimp in the cornstarch mixture until well coated.
Heat 1–2 inches of vegetable oil in a deep skillet to 375°F (190°C).
Fry shrimp in batches for 2–3 minutes per side, until golden and crispy. Transfer to a paper towel-lined plate.
Gently toss the hot fried shrimp with half the bang bang sauce until evenly coated. Reserve the rest for drizzling.
Warm tortillas in a dry skillet.
Layer each tortilla with shredded cabbage, a generous portion of bang bang shrimp, a drizzle of extra sauce, green onions, and cilantro
Serve immediately with lime wedges for squeezing