Bring the granulated sugar, honey and water to a simmer in a non-reactive medium saucepan just to dissolve the sugar.
Add the chopped rhubarb and vinegar, cover your pan, and gently simmer until the fruit is falling-apart soft and the syrup is fragrant and the color of the rhubarb, about 20 minutes. About half way through simmering, give the rhubarb a good stir with a whisk or a fork to ensure it breaks down completely.
Remove the pan from the heat and set it aside, covered, to cool to room temperature.
Strain the shrub through a fine mesh strainer into a clean, swing-top bottle or mason jar.
The method described here results in a nicely sweet-tart, mellow syrup. If you prefer a more tart, vinegar-forward shrub, cook the rhubarb, honey, sugar and 1/2 cup water together for 20 minutes, then remove from heat, add the vinegar and let the shrub cool to room temperature before straining.
Recipe by Northwest Edible Life at http://nwedible.com/rhubarb-honey-shrub/