Your Neighbor Watches As His Dog Poops In Your Yard – What Would You Do

I was doing something in the kitchen two days ago, and I looked out the window just in time to see my neighbor's dog poop in my yard - as he looked up towards my window, the next door neighbors window - saw no one and kept walking.  Now in the loop I live in, most people (including myself) carry bags and clean up after their pet.  Yesterday as I walked my dogs around the loop, my lovely Lucy decided to poop in his yard.  What would you do?  Pick it up or leave it like he did?