Arrange the watermelon cubes on a serving platter.
Place one cube of feta cheese on top of each watermelon cube.
Fold a fresh mint leaf in half.
Insert a toothpick through the mint leaf, feta, and watermelon to create each skewer.
In a small saucepan, combine the balsamic vinegar and brown sugar.
Bring the mixture to a gentle simmer over medium-high heat, stirring continuously.
Continue simmering for about 5 minutes until the glaze reduces by nearly half and slightly thickens.
Remove from the heat and allow the glaze to cool for 1 to 2 minutes. Avoid letting it cool too long, as it will continue thickening.
Spoon a small amount of balsamic glaze over each Watermelon Feta Mint Skewer just before serving.
Serve immediately while fresh and chilled.