Origin of "a hangdog expression of early morning"

Solution 1:

to have a hangdog look or expression

Allen's Dictionary of English Phrases

to look ashamed or dejected. Hangdog was originally a noun and was commonly used as a form of depreciatory or abusive address in the sense 'a miserable fellow fit only to be hanged like a dog'. There is a 17th century use in the current descriptive meaning by the poet and dramatist Thomas Otway in his comedy We Cheats of Scapin (1676): 'A thing of mere flesh and blood, and that of the worst sort too, with a squinting meager hang- dog Countenance, that looks as if he always wanted physick for the worms.'

And the OED has:

Of, befitting, or characteristic of a hang-dog; low, degraded; having a base or sneaking appearance.

As in this earliest recorded usage:

1677 T. Otway Cheats of Scapin:
A squinting meager hang-Dog Countenance.

Even today in Ame, one hears the occasional ~ “Why so hangdog today?”