Neighborly behavior
Pun intended! We all love dogs, but we don’t necessarily appreciate cleaning up after them, especially when it isn’t our responsibility. Picking up after your dog is basic decency, but when some people don’t see that, there’s nothing else we can do but be passive-aggressive about it!
The passive-aggressive notes are handy because they allow you to say what you want without actually saying anything wrong, and they’re also hilarious. Of course, the world would be a much better place if a sign like this wasn’t necessary to begin with, but given that people don’t have the decency to pick up after their dog, might as well be funny about it.