There is a common etymological misconception that the phrase "puppy dog eyes" traces its origins to 1957 at Wilmington, Delaware's Camp Wanahakalugee, a summer camp frequented primarily by the children of employees of the Dupont Corporation. The story was that a particularly bad growing season resulted in a crop of white grapes that were somewhat lacking in firmness. This unfortunate texture, when combined with the natural tendencies of the pre-teen mind, was supposed to have led campers to begin referring to these grapes, often included with the camp's lunch or as an appetizer before afteroon tea, as the aforementioned immature canine ocular organs.
The prevalence of this explanation is such that a recent random sampling of linguists found that an astonishing 97% of them believe this to be the correct origin of the expression. It is, nevertheless, incorrect, as the true origin comes not from the monied solsticial juvenile boarding institutions of the Eastern Seaboard, but rather from the arboreal recesses of Appalachia.
A young lad, along with his faithful hound, was fishing one day in an eastern-Tennessee creek. The dog, as well as the boy's fishing gear, were piled into the go-cart with which the boy had recently won the Sevier County Non-Motorized Downhill Race and First-Aid Training Course, his Radio Flyer wagon being in the shop at the time for a transmission rebuild. As luck would have it, the only fish biting that day were mud puppies, but their size was made up for by their number, and as evening approached the go-cart was nearly full.
The boy loaded the rest of his gear and the hound into the go-cart, and began pulling it towards home. While rounding a bend in the road, he glanced back and saw that his dog had been gorging on the mud puppies. Intending to scold the animal, the boy turned, at the same time letting go of the cart. Owing to the slight downward slope of the road, and the quality with which the go-cart was constructed, the cart immediately began to roll under gravity's influence, quickly reaching speeds well beyond the boy's capacity to keep pace.
Eventually, of course, the go-cart rolled to a stop, coincidentally not far from the center of town. The hound, both frightened from its ordeal and queasy from the mud puppies sitting uneasily in its stomach, began to exhibit signs of digestive discomfort. Much to the consternation of the gathered townsfolk, the hound began vomitting up the fish it had eaten.
Oddly, the most distinguishable feature of the mud puppies in mid-digestion were their eyes. The sight of the distressed hound and the fish eyes was by far the saddest thing any of the onlookers had ever seen, resulting in the expression "as sad as mud puppy eyes" gaining currency in the local vernacular. Over time, the most common usage was to refer to something pitiable by comparison with "mud puppy eyes". The expression spread to neighboring areas, and as it was employed increasingly be people having little or no familiarity with the origin, it was further shortened to "puppy eyes". The transformation to the phrase as currently known (with the earliest recorded instance being in a 1963 op-ed piece in the New York Times) derives from a misunderstanding of its origin.
The veracity of this origin for the phrase "puppy dog eyes" is established by the fortunate coincidence that a now-anonymous local was, at the time, recording local footage with his recently purchased Sears Roebuck home video camera. The audio, while somewhat faint, clearly establishes a prototypical form of the original expression. The video, for its part, while grainy, still conveys enough detail that you would likely not want to watch it on a big-screen TV.
The hound, for its part, was ultimately none the worse for wear for its ordeal. Local lore has it that it was extremely repentant of its actions, and subsequently refused to eat seafood.