We used to call this expression “hangdog”. The photo was sent to me from Dawg’s groomer. He’s just finished being bathed and groomed (two things he hates), and he looks like he’s been beaten and tortured — which, according to his mind, he has. Which is weird since, as I’ve mentioned before, he’s normally a very happy dog.
We don’t see this expression on him very often, and never for very long. It shows up after bathing, after being denied a treat, after being chastised for trying to eat a neighbor’s kid (or their cat) and it symbolizes a long-suffering bewilderment that someone could possibly find anything wrong with his behavior.
It’s sort of, “What’s a saint to do under such a heavy load?” and I can sympathize with him. I feel the same way sometimes. Don’t we all?