Place the vinegar in a small nonreactive saucepan and heat gently. Stir in the sugar and salt until well dissolved. Set aside.
Cut off and discard the chile stems. Cut the chiles lengthwise in half and discard the membranes and seeds. Finely slice. You should have about ½ cup chopped chiles.
Place the chiles in a medium bowl and pour over the warm vinegar mixture. If you have the time, let stand for 30 minutes before serving to allow the flavors to blend. The chiles can be prepared ahead and store in a well-sealed nonreactive container in the refrigerator.