Combine equal parts paprika, cayenne and salt with a dash of sugar on a plate. Moisten the rim and part of the side of a tall glass with lime juice and coat with the spice mix. Combine 2 ounces grapefruit juice, 1/2 ounce each agave syrup and lime juice and a few jalapeño slices in a shaker with ice. Shake, then strain into the prepared glass over fresh ice. Top with a splash of sparkling water and a strip of grapefruit peel.