Add fish sauce, vinegar, sugar, and 1 cup water to a small sauce pot. Bring mixture to a boil. Take the pot off the flame and add minced garlic and chilis. Chill in the refrigerator until ready to use.
Add water to a medium pot. When the water comes to a boil, add shrimp and cook until they turn orange (about 2-3 minutes). Remove shrimp from the pot and slice in half along the backside. Set aside.
Bring water back to a boil and add pork shoulder, add water if needed to make sure pork shoulder is submerged. Cook for 30-45 minutes. Remove pork, rinse, and pat dry. Once cooled, slice thinly and set aside.
Cook rice noodles per package instructions. Drain, rinse with cold water, and set aside.
Assemble the rolls: Wet the rice paper quickly (1-2 dunks should suffice. Too much time in the water will make your rice paper too soggy!) and shake off excess water. On the bottom end of the rice paper, add noodles, vegetables and herbs of your choice, pork belly slices, and shrimp. Start rolling everything up from the bottom. When you are halfway up, fold in the sides. Continue to roll up and you've got yourself a spring roll!