In a cocktail shaker, combine tequila, grapefruit juice, and simple syrup.
Add ice and shake well.
Strain into a martini glass.
Top with a splash of club soda.
Garnish with a grapefruit wedge (optional).
Notes
For a sweeter cocktail, add more simple syrup.Use fresh squeezed grapefruit juice for the best flavor.To make it a mocktail, omit the tequila and add more club soda or grapefruit juice.