Add tequila, lime juice, and agave nectar or simple syrup.
Stir gently with bar spoon.
Pour in grapefruit soda and optional pink grapefruit juice.
Lightly stir to combine without losing bubbles.
Garnish with lime wedge or grapefruit slice.
Notes
For extra tartness, add more lime juice. For a less sweet drink, skip the syrup and let the soda's sweetness shine. Chill the glass before serving for longer-lasting refreshment.