Add about 2 ounces of tequila to two cocktail glasses.
Place 1-2 slices of jalapeño to each glass, depending on your spice tolerance. Lightly muddle the jalapeño. Do not break it apart, just press it to release the oils into the tequila.
Add ice and top each glass off with about 4 ounces of grapefruit soda.
Finish off with a wedge of fresh grapefruit as a garnish.