Crush together the lime segments, chiles, sugar, garlic and cilantro.
Note: Thai chiles can be red or green, are only about 1 1/2 inches long and 1/4 inch or less in diameter. They are on the high end of the heat scale. Find them in Asian markets. If unavailable, substitute fresh cayenne chiles or 1/2 teaspoon, or to taste, of purchased chile sauce, such as sriracha. Fresh chiles can be frozen, airtight, for up to 3 months.