Microwave garlic, oil, red pepper flakes, and sugar in a small bowl until garlic is softened and fragrant, about 40 seconds.
Add 2 teaspoons garlic oil, green beans, and water to a nonstick skillet, cover, and cook until green beans are bright green, about 2-3 minutes. Add remaining garlic oil and cook covered, without stirring, until green beans are spotty brown, about 2 minutes.
Uncover and continue to cook, while stirring, until green beans are crisp tender, about 2 to 3 minutes more. Off heat, stir in vinegar, and season with salt and pepper to taste.