just saying it is possible to get shocked by 12v dc or less. Yes under normal conditions if everything is dry and the car is grounded correctly then there should be very little chance that anyone gets shocked. Now take a hot day when everyone is sweating and has oily/greasy hands on a car that has a ground issue and you would be surprised how easy it is to get a tingle from a car battery. In this case though when he is working with the coil/plugs he is not working with 12v and though and a bad engine/chassis ground could send that coil/plug high voltage seeking ground obviously through the easiest path it can find. You can tell if he got 12v or the high voltage. 12v will tickle and make you say "Hey I got shocked" which normally leads to a conversation something to the tune of "Are you sure?". The coil voltage will sound more like,"YEAAAAWAAAAHUH? What the G-Damn F'ing hell I just got the shtuff shocked out of me!". That normally doesn't lead into the are you sure conversation.......
But in all seriousness tell your assistant to quit being such a damn puss its only electrons AND DO YOU KNOW HOW SMALL THEY ARE?! Get back in and turn the key!!!!!! I would check your battery/chassis ground(right next to the battery) and the chassis/engine ground. By check I mean remove them, sand the area to clean them and then retighten.