Grab a shaker and toss in some ice, 2 shots dark rum, 1/2 Cup passion fruit juice, 1/2 shot simple syrup (to make simple syrup, heat equal parts sugar and water stirring often until sugar is dissolved), and juice of 1/2 lime (about 1/2 shot). Shake to get that stuff nice and cold. Strain into an ice-filled glass, add a splash of grenadine, and put an orange slice on the rim of the glass for garnish.