I wouldn't even be nice about telling him, I'm as subtle as a brick to the face when someone needs educating on the error of their ways!
Someone at my club had their really expensive rifle in a vice type setup the other week and was literally not touching the gun only their finger pulling the trigger, I sat there and observed, noticed the grimace come across his face when I pulled a HW35 from its bag that had been lent to me by a valued friend. I then proceeded to smash the bull to ribbons in front of him at 30 yards, went and collected my target and just smiled at the bloke! Then said "