If the guy knew what would happen and had tested it, a good lawyer could get him off with disorderly conducy, or less.
regards.....casey
BTW: some off worst shocks I've receiver were from GFCI's.
Make sure the breaker is off when placing thumb on white line screw, and index finger on gold line screw to position GFCI into plaster ring. The current on the line side does not go through the sensory circuit, so all current passes in your hand, OUCH.
When placing said fingers on the load screws, if NO IMBALANCE appears, once again, OUCH! No Imbalance, No Trip!
GFCI will trip ONLY if some current from load HOT side passes to a ground point other then load neutral cuasing the imbalance.