Mix the mayonnaise, sweet chili sauce, and sriracha in a small bowl. Chill the sauce in the refrigerator.
Marinate the shrimp in buttermilk for 10 minutes. In a separate dish, mix the cornstarch with salt.
Remove shrimp from buttermilk, letting excess drip off. Coat them in the cornstarch mixture.
Heat the oil in a deep fryer or large pan to 375°F (190°C).
Fry the shrimp in batches until golden and cooked through, about 2-3 minutes per batch.
Drain the shrimp on paper towels. Toss them in the chilled sauce until evenly coated.
Serve the shrimp immediately with extra sauce on the side for dipping.