Toast the shredded coconut in a skillet over medium-low heat, stirring constantly until most of the coconut is golden-brown (about 5 minutes). Remove from the pan and cool completely.
3 tablespoons unsweetened coconut
Transfer the toasted coconut to a plate. Add the syrup to a separate plate.
2 tablespoons agave nectar
Dip the rim of the glasses into the syrup, then roll in the toasted coconut. Let the coconut set for at least 1 minute, while you prepare the drink.
For the Drink
Add all of the drink ingredients to a blender and pulse a few short times, until just combined.
1 cup water, ½ cup sweetened condensed milk, 5 ounces coconut rum, ¼ cup freshly squeezed lime juice
Add ice to cocktail glasses. Pour the drink over the ice and add a lime slice to each. Serve immediately.
Notes
Don't over-blend or it will become foamy. You just need a few short pulses to combine all of the ingredients. Alternatively, you can mix it with a spoon in a pitcher or glass.
I like to let the drink sit with the ice for a few minutes so it gets nice and cold. You can also chill the glass and liquid ingredients beforehand to get it chilled quicker.
I don't recommend storing the drink in the fridge for longer than a day as the ingredients will start to separate.