To make a graffiti mop, you will need an empty plastic bottle, a marker or tape, a pair of scissors, a sponge or a cotton mop head, and ink or paint. Start by marking or taping off the nozzle of the bottle to create a small opening. Using the scissors, cut off the top part of the bottle. Next, insert the sponge or cotton mop head into the bottle, filling it about halfway. Pour the ink or paint into the bottle, allowing it to saturate the sponge or mop head. Finally, test your graffiti mop on a surface before using it for your artistic pursuits.