To make the simple syrup, add sugar, water, and jalapeño slices to a small saucepan. Bring the mixture to a boil. Turn down the heat and allow the mixture to simmer until the sugar dissolves. Remove from the heat and cool to room temperature. Strain and transfer to an airtight container. Syrup will stay fresh in the refrigerator for up to 1 month. 

To make the margarita, add ingredients to a cocktail shaker. Add ice and shake vigorously for a few seconds. Divide between two glasses filled with ice. Garnish with a sprig of mint (or cilantro), lime wedge, jalapeno slice, and pineapple wedge.