Usually pick it up myself and “look” at the person. Unless it is dog poop, then I hold out a spare bag, say, “Oh, do you need a poop bag?” and just stand there.
I used to pick it up and tell them they dropped it, but now I don’t bother. Sometimes I’ll pick it up myself, other times I leave it, depending on my mood.
Always I make a pained grimace and feel a surge of annoyance. If I know the person, snark and/ or haranguing ensues. If I don’t, usually I’ll just pick it up myself.
I call people out on it. That’s just something that is not okay with me. I make an effort to swing my bike lock while I’m doing it. That usually helps.
Here’s an approach that might work, once my friends mom saw a girl throw a bag on the sand, so she chased her down and made her throw it away, haha. Make them learn their lesson ;]
I also ask them if they dropped something, if they say no then I insult them. If they get hostile then I rally the people around me to make that person uncomfortable. This always works for me, it’s harsh but effective. Especially if it’s dogg poop, that’s disgusting.
I was at a festival, and a man lit up a cigarette, took a puff on it and dropped it on the ground 5 feet from a trash can. I told him to step on it, then put it in the trash can. He picked it up and walked off, shaking his head. I’m not sure why he was mystified. Was he looking to drop it somewhere else, did he plan to smoke more of it and drop it somewhere else, or was he simply too stupid to get the point?