Rinse as much paint out of the garment as you can with warm water. Do not rub the paint, just let the water pour over it. Turn the garment inside-out and rinse from behind the stain.
Moisten a paper towel, then dip it in some Murphy's Oil Soap. Blot the stain, with the garment right-side-out, with the paper towel. Do not rub the paint, just dab at it.
Rinse the painted area from both sides with warm water. Repeat the process until the stain is gone.