Stir together mayonnaise and Sriracha in a small bowl. Cover and chill.
Soak calamari in buttermilk; chill at least 1 hour. Combine flour and next 3 ingredients in a medium bowl. Remove calamari from buttermilk, and dredge in flour mixture. Shake off excess, and separate rings and tentacles.
Pour oil to depth of 2 inches into a Dutch oven; heat to 365°. Fry calamari, in batches, 1 minute or until done. Drain on paper towels, and serve warm with spicy mayonnaise.