All you do is combine 1 cup of sliced blueberries with 1/8 of a cup of sugar:
Allow to sit overnight and render juice. Push the juice and remaining berries through a strainer or a mill until the solids are completely separated from the liquids.
It looks weird, but you can use the remaining solids to top ice cream, oatmeal or anything else that would benefit from a sweet and fruity topping!
After you have your liquid, add one 1 TBSP red wine vinegar. Some folks will tell you to add more vinegar, but I think 1 TBSP is plenty and won't make your cocktail taste like salad dressing.
That's it! Now you're ready to make your Blue Friday (or any other) cocktail!
Blue Friday Cocktail
2 oz light rum
1 oz blueberry shrub
1/2 oz fresh lime juice
Shake with ice and strain into a cocktail glass!