In a blender, blend all of the ingredients until the mixture reaches a smooth consistency (30-60 seconds). The texture should be similar to a slushy, but it will melt within a minute and become drinkable as you serve it. If you feel like it's too thick, you can always add a tablespoon of water to thin it out a little.
Pour into 2 Margarita glasses and serve.
To make the simple syrup: Combine equal amounts of sugar and water in a saucepan, heat until the sugar has dissolved in the water. Remove from heat, and let it cool down (or place in the fridge).Feel free to add more rum. After blending the cocktail, have a taste and see if you would like to add more alcohol, lime, or sugar syrup.