I totally sympathise. I've had people stand on their porches and glare at Syd and I because she was sniffing their lawn (not even standing on it). Makes me want to yell "She pooped before we left the house...you can relax!" at them.
It's unfortunate that there are ignorant pet walkers out there that don't pick up their dog's poop that make people wary of every dog that walks by.