Snap off the tough ends of asparagus and wash asparagus thoroughly. Cook asparagus in boiling water for about two minutes, until it’s bright green and just beginning to get tender. Drain. Place asparagus in a large bowl of ice water to stop the cooking. Drain. Lay asparagus in a 13″ by 9″ baking dish. In a small bowl, whisk together the olive oil, balsamic vinegar, sugar, garlic, and red pepper flakes. Pour over asparagus. Cover dish with plastic wrap and place in the refrigerator. Chill for about 8 hours. Using tongs, remove asparagus from marinade and serve.