In a small bowl, whisk together the mayonnaise, Thai sweet chili sauce, and sriracha. Set aside.
In a medium bowl, combine buttermilk, salt, pepper, onion powder, and garlic powder.
Add the shrimp to the marinade and stir until evenly coated.
Heat 1½ inches of oil in a heavy pot or Dutch oven to 375°F (190°C).
Remove shrimp from the marinade one at a time, allowing excess liquid to drip off.
Coat each shrimp thoroughly in cornstarch and shake off any excess.
Fry the shrimp in batches for 2½–3 minutes until golden brown and crispy.
Transfer cooked shrimp to a paper towel-lined plate.
Place warm shrimp in a large bowl and drizzle with half of the Bang Bang sauce.
Toss gently until evenly coated and let rest for 10 minutes.
Warm the tortillas on a skillet or griddle for about 30 seconds per side.
Fill each tortilla with cabbage, diced tomato, and Bang Bang Shrimp Tacos filling.
Drizzle with the remaining sauce.
Garnish with cilantro and serve with fresh lime wedges.