Shell and clean your shrimp, leaving the heads on. Lay the shrimp out on a plate and squeeze the lemon juice on top, followed by some salt, black pepper, chili flakes, if using, and a good splash of olive oil (this will partially cook the shrimp). Let the shrimp marinate 10 minutes, if desired, or serve immediately. Garnish with fresh parsley.
Warning: Consumption of raw or undercooked shellfish may substantially increase the risk of foodborne illness.