For jalapeño tequila: add 2 sliced jalapeños to a large jar or container and cover with 1 1/2 cups of tequila. Let sit for 24 hours, then strain before using. Keep in a sealed container for a few weeks, preferably in the fridge.
For mango simple syrup: combine equal parts sugar and water (I suggest 1 cup of each), bring to a boil and let sugar dissolve, then turn off heat and let cool completely. Combine 1 cup simple syrup + 1/2 mango (peeled and cubed) in a blender and blend until combined.
To make the margaritas, rim the ridge of your glass with a lime wedge and dip in margarita salt. Fill the glass with ice. In a cocktail shaker, combine tequila, grand marnier, simple syrup and lime juice with ice, and shake for about 30 seconds. Pour over ice and squeeze in lime slices. I also took a few of the jalapeños from the tequila and removed the seeds, then toss them in the margarita.