Make the coleslaw topping: In a large bowl, combine all the slaw ingredients (cabbage, scallions, cilantro, mayonnaise, sour cream, and lime juice). Toss to combine evenly, and season with salt and pepper to taste. Set aside.
Make the bang bang sauce: In a medium bowl, whisk the mayonnaise, Thai sweet chili sauce, and sriracha until evenly combined. Set aside.
Pat dry shrimp and season with ½ teaspoon Kosher salt and ¼ teaspoon ground black pepper. Toss the shrimp in buttermilk. Set aside.
Heat oil (about 2 inches deep) in a heavy duty pan until the oil’s temperature reaches 350 to 365 F. Use a candy thermometer to check the temperature.
As the oil nears the right temperature, toss the buttermilk-coated shrimp with cornstarch (a few at a time, leave excess buttermilk behind), pressing gently so the cornstarch sticks well.
In batches, cook shrimp in batches for about 4 minutes until crispy and golden brown. Transfer to a plate lined with paper towel to soak any excess oil. Repeat with the remaining shrimp. Note: the oil temperature will drop when you add food - you can increase the heat to bring it back to temperature.
Toss the fried shrimp with about half or two-thirds of the prepared bang bang sauce. Save the rest of the sauce for serving.
Assemble: Top each warm flour tortilla with about 2 pieces of the bang bang shrimp. Top with the coleslaw and serve with a fresh squeeze of lime juice and a good drizzle of the bang bang sauce. Serve immediately and enjoy!