Add watermelon and pinch of salt to a small bowl. Mash watermelon using a potato masher until pieces are small enough to fit through your straw (or - if you're lazy - you could use a blender). Pour watermelon mash into your favorite water bottle (or a large glass). Add tequila, ice, and club soda. Stir gently. Makes 1 serving (even tho the title is plural). You can share if you want, but I don't recommend it.