In a bowl combine cherries and sugar. Mash with a fork. Let sit 24 hours in the fridge. You can let it sit up to 3 days.
Strain the cherry mixture with a fine mesh strainer. Add apple cider vinegar. Whisk to combine until sugar is dissolved. Pour into a jar and store in the fridge.
Notes
This cold process shrub will last for about 6 months in a glass jar in the fridge.