Pour 1 cup (240 ml) of white vinegar into a pot or pan and wait for it to come to a boil. Boiling the white vinegar should only take a few minutes. Dip a clean rag into the white vinegar carefully, making sure that it’s wet but not completely saturated. Rub the overspray spots with the rag. The hot white vinegar helps to loosen the overspray from the glass surface.  Wear rubber gloves to prevent the hot vinegar from hurting your hands. Some of the overspray may come right off after you rub, while other spots may still stick, which is OK. Find a small bucket or bowl with warm water. Pour a few squirts of soap into the water, or enough to make it sudsy. Dish soap is ideal, but you can also use hand soap as an alternative. Dip a clean rag into the sudsy water and wet the overspray spot. The soapy water should coat the surface and will help prevent it from being scratched by the razor blade. Find a razor blade — a new one is best, but as long as it isn’t dull or caked with dirt, it should work — and position it on the overspray surface at a 45 degree angle. Scrape the overspray off carefully in a slow motion, making sure to keep the razor blade at an angle to prevent the surface from being damaged. Wet the overspray spot with the sudsy cloth if it dries out before you’re able to use the razor blade. Spray a few squirts of glass cleaner onto the surface that you just scraped. Use a clean rag or paper towel to wipe off any extra paint or dirt, ensuring your glass is clean and dry.

Summary:
Boil 1 cup (240 ml) of white vinegar in a pot. Dip a clean rag into the vinegar and wet the overspray spots. Fill a bowl with warm water and soap. Wet the overspray spots with a sudsy rag. Scrape the overspray off with a new razor blade. Spray the glass with a glass cleaner to clean off any residue.