Begin heating corn oil in a heavy skillet on medium-high heat. Coat pan with about ¼ inch of oil. Mix flour, garlic powder, and pepper in a plastic bag. Cut calamari tubes into ½ inch rings. Add calamari rings and tentacles into the plastic bag and shake until they are evenly coated. Shake off excess flour.
Place an even layer of calamari into the skillet once oil is very hot. Cook until golden brown (approx. 90 seconds). Remove calamari rings and tentacles from skillet and set aside on paper towels. Repeat as needed.
While calamari is cooking, in a separate skillet combine chopped garlic with oil, peppers, pepperoncini juice and heat. Add all cooked calamari rings and tentacles, then toss until evenly coated. Remove and serve immediately.