In a medium saucepan, combine 2 cups of apple cider vinegar, 1/2 cup of ketchup, 1/4 cup of brown sugar, 2 tablespoons of Worcestershire sauce, 2 teaspoons of salt, 1 teaspoon of black pepper, and 1 teaspoon of red pepper flakes.
Whisk the ingredients together until the brown sugar has dissolved and the mixture is well combined.
Place the saucepan over medium heat and bring the sauce to a simmer.
Reduce the heat to low and let the sauce simmer for about 10-15 minutes, stirring occasionally until it has thickened slightly.
Taste the sauce and adjust the seasoning as needed. If you want a sweeter sauce, you can add more brown sugar. If you want a spicier sauce, you can add more red pepper flakes.
Once the sauce has reached your desired consistency and flavor, remove it from the heat and let it cool.
Store the sauce in an airtight container in the refrigerator until ready to use. The sauce can be made ahead of time and will keep in the refrigerator for up to a month