Using a paring knife, cut through the back shell of each shrimp and remove the dark vein. Run you forefinger between the shell and flesh of each shrimp, separate but not removing shell from flesh. 

In a large bowl, whisk the sugar, fish sauce, lime juice, hers, oil garlic, and chiles until sugar is dissolved. Place shrimp and marinade in a large zipper-top plastic bag. Squeeze out the air, seal, and shake to coat the shrimp evenly. Refrigerate fo 4 hours, turning the bag every 30 minutes.

To cook the shrimp, prepare a grill for high heat grilling. Remove the shrimp from the marinad and grill, turning frequently, for 2-3 minutes, until evenly pink and golden on both sides. Serve, passing a bowl for the shells at the table.