This a tough one. You state he is your elderly neighbor, so that procludes you from going next door, dragging him into your yard and cramming the leaves back up his ass. So my suggestion is to rake all the leaves up, bag them and get rid of them, then go inside and bake a dozen or so chocolate chip cookies using chocolate Ex-Lax in place of the chips. Deliver them to your neighbor, sweetly saying, "Pleae try not to blow all your leaves into my yard again and to show there are no hard feelings, here are some fresh baked cookies." Then go home, crack a beer and sit back smiling to yourslef knowing that revenge is sweet and in this case pretty damm messy!