Place vinegar, water, salt, and sugar in a saucepan and bring to a simmer. Turn off heat and cool slightly.
To each quart jar, add 1 garlic clove, 1/8 teaspoon red pepper flakes (optional), a few onion slices, a few jalapeno slices, and 3 eggs. Repeat each layer with onions, jalapenos, and eggs. Continue until the jar is full. (I was only able to get 11 eggs in each jar because my eggs were large)
Pour the liquid over the eggs and seal the jar. There should be enough liquid for 2-quart jars.
Refrigerate at least 3-4 days before eating. These eggs will last for 1-2 months in the refrigerator. Mine never last that long.
Notes
Note: If you find you need additional liquid to fill the second jar, add a little more vinegar or water to the jar.You are not canning/sealing the jar; therefore, there is no need to sterilize the jars and lids before filling. These will be stored in therefrigerator, not on the pantry's shelf.