In a bowl, combine the lemongrass, fish sauce, lime juice, brown sugar, vegetable oil, garlic, red chili flakes, and black pepper. Mix well to create the marinade.
Add the shrimp to the marinade, ensuring they are well coated. Cover and refrigerate for at least 30 minutes, or up to 2 hours for more flavor.
If using wooden skewers, soak them in water for 30 minutes to prevent burning.
Preheat the grill to medium-high heat.
Thread the marinated shrimp onto the skewers, leaving a little space between each shrimp.
Place the skewers on the grill and cook for 2-3 minutes on each side, or until the shrimp are pink and opaque.
Remove from the grill and let rest for a couple of minutes before serving.