Rub the rim of a 10 oz. glass with a grapefruit wedge; dip in margarita salt to coat. Fill the glass with ice. Next, fill a cocktail shaker half full with ice. Add 1/4 cup fresh red grapefruit juice, 3 tablespoons tequila and 1 jalapeno pepper slice. Cover with lid & shake vigorously until thoroughly chilled, about 30 seconds. Strain into the prepared glass. Top off with a citrus soft drink, such as Squirt. Garnish with a red grapefruit wedge and a jalapeno pepper slice, if desired.