First off, I think it's important that I make it perfectly and crystal clear that I don't know what the obvious thing to do is.
This question is like a maze, within a trap with one of those sticky floors. It's hard to navigate an actual answer, because you used the word stoop in conjunction with the act of shitting. This is funny for many, many reasons.
1 - Now I'm picturing the man stooping as he shits on my porch.
2- Stoop is one letter away from stool, which is what the man is leaving behind.
3- Stoop sounds like poop, which is what the man is doing/leaving behind.
You get the drift.
I guess it all depends on my neighbor's motivation. If he's doing it because he's super drunk, than I probably wouldn't do anything but get the hose. But if this was a vengeful or malice filled stoop pooping, I would be inclined to ask him to clean it off himself, or with his wife's filthy whore face.
Moving forward, I would dislike him.
Short Answer: Boom! Take that, neighbor who shits in a strange position!