I always like to use fresh citrus juice but if fresh grapefruits aren't available, store-bought pink grapefruit juice will work as well. Should you want the slush to be more gin-forward, use the larger amount of gin. If you're not a fan of gin, vodka will work in its place, as would tequila, which a reader mentioned in the comments. (Thanks!) This slush very refreshing on its own, but would make a nice dessert topped with fresh raspberries tossed in a little sugar. In the winter, you can garnish it with orange and grapefruit sections, as well as sliced kumquats. No matter what the season, if you want to splash a little extra gin (or a bitter aperitif, such as Campari) over it, be my guest.