Add tequila and jalapeno to a clean, lidded container. Shake to combine and allow the flavors to meld for 12-24 hours, depending on how spicy you'd like it. Once the flavor has developed, strain the jalapenos and discard.
The tequila will keep for up to 1 year. I like to store mine in the freezer.
Cut pineapple into 1 inch thick rings, discarding the rind.
Preheat grill to medium-high and oil it lightly. Grill pineapple for 4-5 minutes on each side, until you get nice grill marks and it begins to soften slightly.
Place the grilled pieces in a bowl and allow to cool completely in the refrigerator.
Add jalapeno infused tequila, triple sec, 2 slices of the grilled and chilled pineapple (and any juices that have accumulated in the bowl), lime juice, agave, vanilla extract and water to a blender. Process until smooth. If desired, strain to remove the pulp from the pineapple.
To salt the rim, run a lime slice or pineapple wedge around the lip of your glass and dip into salt to cover.
Add crushed ice to your glass, pour in your margarita mixture, and garnish with extra grilled pineapple, jalapeno slices or lime wedges.