Place the shrimp in a large bowl and pour the buttermilk over them. Let the shrimp soak in the buttermilk for about 5 minutes.
In another bowl, mix the flour, garlic powder, paprika, cayenne pepper, salt, and black pepper. Stir until evenly combined.
Remove each shrimp from the buttermilk, allowing the excess to drip off, and then dredge them in the flour mixture, making sure they are coated evenly.
Heat 3 inches of vegetable oil in a deep frying pan over medium-high heat. The oil should reach 350°F.
Place the shrimp into the hot oil, a few at a time, being careful not to overcrowd the pan. Fry for 3 minutes per side, or until golden and crispy.
Remove the shrimp from the oil using tongs or a slotted spoon, and place them on a paper towel-lined plate to drain excess oil. Serve immediately.
Mix together mayonnaise, ketchup, hot sauce, and lemon juice in a small bowl. Serve with the fried shrimp for dipping.