Wash the peppers, trim off the stems, and slice them into rings about 1/4-inch thick
Shake out the loose seeds if you want less seeds
Pack the rings into a clean quart jar with the garlic
Bring the vinegar, water, salt, sugar, and red pepper flakes, if using, to a boil, stirring until the salt and sugar dissolve
Pour the hot brine over the peppers until they're covered, leaving about 1/2 inch at the top
Press the rings down with a wooden spoon to push out air bubbles
Let the jar cool to room temperature
Put the lid on, and refrigerate
They're ready to eat in 24 hours and best after 2-3 days
Keep them in the refrigerator for up to 2 months