Cut the tops off the strawberries and quarter them. Put the strawberries, rhubarb, sugar, and vinegar in a pot with a tight-fitting lid (a lid helps keep all aromatics in the shrub). Bring to a gentle boil over medium-low heat; boil for 5 minutes. Remove from heat and let cool. Once cooled, blend the mixture in a blender, then strain through a fine-mesh sieve.
Pour 2 oz. of the strawberry-rhubarb mixture into a collins glass, add ice to the top, then finish with club soda or tonic.