Special equipment: a deep-frying thermometer
For the sriracha mayonnaise: In a small bowl, whisk together the mayonnaise and sriracha until completely blended. Set aside.
For the fried okra: In a deep heavy-bottomed pot, heat about 6 cups of oil over medium heat to 350 degrees F.
Pour the buttermilk into a medium bowl and add the okra, tossing it to coat the okra. In a separate bowl, combine the cornmeal, flour, garlic powder, salt, black pepper and cayenne and whisk to combine.
Working in batches, use a slotted spoon to transfer the okra to the flour mixture and toss well to coat. Using a wire mesh skimmer, slide the okra into the hot oil. Fry until golden brown, about 5 minutes, stirring to fry evenly. Use the skimmer to remove the okra to paper towels to drain.
Serve immediately with the sriracha mayonnaise dipping sauce.
These proportions are for a moderate level of heat. Adjust for more heat by adding more sriracha; adjust for less heat by adding more mayonnaise.