In a medium size bowl, add the tajin, salt and sugar and mix well. Next pour mixture onto a plate and set aside.
Rub the rim of the margarita glass with a wedge from the lime to make it moist, dip the rim of the glass in the salt, sugar mixture on the plate, and set aside
In a large mix drink shaker add the watermelon juice, Cointreau, tequila jalapeño slices, lime juice and ice. Shake until the shaker feels ice cold to the touch. Pour into your margarita glasses and serve.
