Make the simple syrup. Add the sugar and water to a small sauce pan and place it over medium-high heat. Heat just until the sugar has dissolved, then pour this into a small bowl to cool.
Peel and pit the rambutans. Make a small incision at the top to get started. Carefully remove the thin skin from the fruit.
Using you fingers, dig into the fruit and remove the pit.
Place the rambutan in a cocktail shaker and muddle only until they are broken enough to release their juices.
Add the vodka, lime juice, vanilla, ice, and cooled simple syrup. Cover and shake vigorously for 30 seconds.
Strain into two martini glasses, adding a few pieces of broken rambutan flesh. Enjoy!