I would have picked up the poop in the plastic sack in his yard, and then just left the plastic sack (weighted down) to stay in his yard until whenever he decided that darned sack needed to blow away and wasn't. We have idiots like this in my neighborhood. I would never approach their homes to place the bags on their front doors, but believe me, trash up their yard a few times (by watching intently for other dog poops while walking by) and anchor them in their yards.....they'll get the message! (Or maybe finding a few 'extra deposits' while on your walk and littering his yard with plastics bags), believe me, even a blowhard will get the clue.