Maybe I'm being unreasonable, but it drives me flipping nuts when people bag up their dog's poo and then leave it either on the pavement or - worse - on my garden wall! I mean, there are always bins around, even in people's gardens, can't they put it in there? Oh, and sometimes the bag isn't even tied 
So, should I put a passive-agressive note on the wall or keep picking up the bags and putting them in my own bin? Or just get over it...?