Place 2 whole jalapenos and the tequila in a small bowl. Cover with plastic wrap and set aside for 1 day.
Pour the tequila into a pitcher or large punch bowl and add the lime juice, Cointreau or Grand Marnier and the guava juice. Stir to combine and chill in your refrigerator.
Place the coarse salt or margarita salt on a flat plate. Rub a lime wedge around the rim of each glass, turn it upside down on to the salt and then twist the glass in the salt to coat the rim.
Thinly slice the remaining jalapeno. Using a paring knife, remove the seeds from each slice. Serve the margarita straight up in a martini glass with some jalapenos floating in the glass or slit one side of the jalapeno ring and hang on the side of the glass.