It is sometimes possible to remove paint from plastic using a paint scraper and a gentle touch. Many of the solvents normally used to remove paint from metal or wood damage plastic, making them an inappropriate choice.
If the scraper does not work, rubbing a small amount of cooking oil on the paint helps loosen it for removal. Fingernail polish remover and denatured alcohol are stronger choices but require testing in an inconspicuous spot first.
The job sometimes requires the help of a professional. If spray paint finds its way onto the plastic lenses of eyeglasses, return them to the optician for removal of the paint to prevent damaging the optical quality of the glasses.