[morzh]

The reason he is not getting knocked on his butt is probably because he is standing on an insulating surface, like a wooden floor or a carpet, and maybe not on the ground floor. And he is not touching the chassis with the other hand at the same time.

Still.....unless you are a pro or a very experienced person in elecrtricity, I would advise not to touch ANYTHING with your bare hands, even the chassis unless you are working off of an isolation transformer. Then you can touch anything. With one hand, keeping another one in your pocket.