Pour the coconut syrup over the ice and let it pool before the soda goes in.
Tilt the glass and pour the grapefruit soda slowly down the inside wall, stopping when the fizz climbs near the rim and settles back.
Pour the half-and-half over the back of a spoon so it clouds the pink soda into soft gold streaks.
Stir once, hook the grapefruit wedge onto the rim, and serve immediately.
Good to Know
This is the combination to point toward adults who want something less sweet; it is the closest thing on the bar to a bitter aperitivo, minus the alcohol.