Start by cold-steeping coarsely ground coffee in 4 parts water for 12 hours. Room temperature is fine, but it will work in the fridge. Then filter using a French press or standard filters. The steeped coffee can be mixed with 2-3 parts cold water/milk/soy and sweetened to taste. Then bottle and carbonate. Alternately, sweeten the mix and add it to carbonated water.
Remember one unassailable statistic, as explained by the late, great George Carlin: "Just think of how stupid the average person is, and then realize half of them are even stupider!"
"I would like to die on Mars, just not on impact." Elon Musk