Do NOT use fingernail polish remover (acetone). It will probably slime the paint off, but it will deform the plastic too.

Some cheap spray paint won't bond to plastic, hardly at all. If you are so fortunate, it may actually peel off if you can get it started. It may help to submerge the affected plastic pieces in water for a great deal of time. This may loosen the paint allowing for said peeling process.

Submerging in alcohol would be ideal but cumbersome. Maybe coating it with strong alcohol, and reapplying to keep it wet for a while may also loosen it enough to peel.