Add water, muddled hot cherry pepper, sugar and agave in a small pot and bring to a boil. Lower heat and simmer for 5 minutes. Remove from heat, strain and cool.
Fill a cocktail shaker with fresh ice. Add tequila, grapefruit juice, lime juice and 1 oz prepared hot cherry pepper simple syrup. Cover and shake vigorously.
Serve in a tall glass over ice with a turbinado sugared rim.
