Dip rim of a glass in agave nectar then tajin and add ice to glass.
Add jalapeños, agave syrup and lime juice to cocktail shaker and muddle.
Add ice, grapefruit juice, tequila, and triple sec to cocktail shaker.
Shake and strain over glass with ice.
Garnish with sliced grapefruit, jalapeño slices, and/or lime wedges.