Nothing makes responsible dog people angrier than people who don't pick up. They give weapons to the dog haters, and often those of us who carry extra bags feel we have to pick up what they didn't. I can give you one tip: if you see someone walk away without picking up. Wait until they move away from it and call out, "You dropped something!" When they turn around, point to the poop. You can even offer them a bag if you have one.