Avocado Pickles

In a small saucepan over medium heat, combine vinegar, water, sugar and salt and bring to a boil, stirring frequently. When the sugar and salt have dissolved, set aside to cool. In a mason jar, place red pepper flakes, garlic, cilantro, and avocado slices. Pour cooled pickling mixture into the jar and seal tightly with a lid. Refrigerate for at least 3 hours before serving.