Dried paint stains are a nightmare to remove, but WD-40 can make the task quicker and easier, as its degreasing power can lift the paint pigment without damaging the surface.
First, wear gloves to avoid the dangers of prolonged skin contact with WD-40. If you're tackling a large project with it, especially indoors, you should also wear a mask.
To remove the dried spray paint from solid surfaces like metal, plastic, or glass, spritz WD-40 onto the paint stain, let it sit for up to a minute, and then scrub with a cloth.
For rougher exteriors, like concrete, use a hard-bristle brush instead of a cloth or paper towel. You can also let the WD-40 sit longer, about five to 10 minutes, before scrubbing.
If the dried paint marks are from oil-based paints and on your clothes or fabric, apply WD-40 to the entire stain, blot with a sponge, and then use a cloth to wipe the area.
For carpets, let the WD-40 soak in for 20 to 30 minutes before scrubbing with a cloth. Repeat if the stain persists, then wash with dish soap, and rinse with warm water.