Combine vinegar, water, oregano, red pepper flakes, salt, and garlic in a medium pot and bring to a boil
Turn off heat and add jalapeño rings. Stir frequently for even cooking and let it sit in the hot liquid for 10 minutes.
Load rings inside of two large jars and fill to the top with cooked vinegar mixture.
Let it cool for 10 minutes, put lids on jars, and store in the refrigerator for a minimum of 24 hours. These can be stored for up to 2 weeks in the refrigerator.
Notes
For sweeter or less hot jalapeños, add 1 Tablespoon of organic cane sugar to pot with vinegar mixture and bring to a boil. The sugar makes it slightly sweet and cuts down the heat quite a bit!