The man says it, pulling his two big dogs back from the mouth of the alley. I don't know what kind of dogs they are; I'm not a dog guy. I know there are big ones, I know there are small ones, and I know there are wiener dogs. This guy has two big ones.
A car has emerged from the mouth of the alley without the obligatory honk to announce its presence. The man has been walking his two big dogs down the sidewalk and they, being two big dogs and therefore dumb and slobbery beasts, haven't stopped as the car slowly cruises out of the alley. They aren't hit, clipped, or hurt at all. The car simply passes uncomfortably close to them as it cruises past and onto the street.
It doesn't stop at all. The driver looks to his left to see if any other cars are coming, then continues to pull into the street. Maybe he looks at the dogs, maybe he looks at the dog-walking man, I can't tell. But the man pulls on the reins of his dog-shaped horses and they step back, but even with a large roving rectangle of steel before them they don't seem to understand why. The man is confused too, if only for a moment, and then he scowls at the breaklights of the car and yells.
I don't know if the driver hears him, but I doubt it. I think that's the point.
Grocery stores are terrible places to maneuver in, especially if you're pushing one of those large metal carts with at least one bad wheel. There is no code of conduct to cart-pushing, no rule that says you have to walk down one side of the aisle, no proper etiquette for how long one can linger in front of the Cap'n Crunch. You're always deftly avoiding someone's cart or someone's kids, constantly swerving around an old woman who can't decide what brand of Ginger Ale to buy this week. But I've never in my life seen someone be cut off in a grocery store and yell, "You CUNT." Not even when jockeying for a place in line. Because there is an immediacy to it, the chance that the Cunt will turn around and punch you in the mouth.
When you are in your car, or the Cunt is in theirs, there is very little chance the Cunt will stop what they are doing, park, get of the car, and confront you. This is interpreted as an excuse to forget the constraints of civility, or simply a reason to let out the stress and anger one cannot reveal when cut off in line at the grocery store. When there is little chance of being held accountable for one's actions, the truth of someone's personality and inclinations can be seen.
But I don't see what's wrong with reining your dogs in, laughing and being thankful the driver wasn't speeding through the alley, and petting your dog on the head. Give him an extra bone when you get home, or a child's leg, or whatever it is dogs like to play with. Save "You CUNT" for your friends, family, and co-workers. Chances are they've done something to actually deserve it.