The oil and sugar give the marinade some viscosity so it doesn't just season the shrimp but clings to it.
Mix together the Sriracha, olive oil, Worcestershire sauce, garlic, cilantro, and sugar. Season aggressively with salt and pepper. Put in a 1-gallon plastic bag, add the shrimp, and mix together in the bag. Marinate in the fridge for 2 to 4 hours, or longer.
Heat a grill. Skewer the shrimp (4 to 6 shrimp per skewer) and grill until pink and delicious, 2 to 3 minutes per side. Remove the shrimp from the grill, slide the shrimp from the skewer using a fork, and pile on a serving platter. Sprinkle with finely chopped cilantro, and spear toothpicks in a few shrimp. Watch them disappear.