Add the orange juice in the glass so it fills it about 1/3.
Then take a napkin and put it over the glass pushing it down toward the juice.
Push napkin down as far as it can go without touching the juice.
Next pour the vodka very slowly so it dribbles on top of the juice.
This will create a layer of vodka that lays on top of the juice because of the different densities of the liquids.