Pour the grenadine into the base of a tall glass and set aside. Fill a cocktail shaker with ice and add the tequila, triple sec and fruit juices. Shake until the outside of the shaker feels cold.
Add a few ice cubes to the serving glass then carefully double strain the cocktail into it, trying not to disturb the grenadine layer too much. Add more ice if needed to fill the glass then garnish with a cherry on a stick or cocktail umbrella.