Muddle the limes in a shaker. Add the rum, Simple Syrup and vodka. Fill the shaker halfway with ice and shake for 8 to 10 seconds. Strain into a 14-ounce Collins glass. Garnish with the scorpion lollipop.
Put the sugar and water in a small saucepan. Cook over low heat, stirring, until the sugar dissolves. (Alternatively, heat in the microwave.) Store in a sealed container in the refrigerator.
Recipe courtesy of John Green