Lay the pen stained dress shirt on a flat work surface with the pen stain facing up. Wet a cotton swab with rubbing alcohol. Sponge the outer rim of the ink stain with the rubbing alcohol to prevent the ink from spreading into the surrounding fabric.
Blot the rest of the stain with rubbing alcohol. Allow the rubbing alcohol to sit on the surface two to three minutes. Lay a paper towel beneath the stain on the shirt and press another dry paper towel onto the ink stain to lift the ink. Continue this process to remove as much of the pen ink as possible.
Discard the paper towels and squirt white toothpaste onto the remaining ink stain. Rub the toothpaste into the stain then rinse it out with cool water. Repeat this step two more times to remove as much ink as possible.
Mix 1/2 cup of all-fabric bleach with 1 gallon of water. Soak the pen stained dress shirt in the diluted bleach solution for 30 minutes to loosen any remaining ink stain.
Wash the shirt with heavy duty laundry detergent and all-fabric bleach. Before drying the shirt, ensure the entire ink stain was removed as heat from the dryer will set the stain. If any ink remains in the dress shirt, soak the shirt in the all-fabric bleach solution again before washing a second time.