How did the term "drunk as a skunk" come about?

You've heard the expressions "stinking drunk" and "stinko" ("stinking" has been used in English to express disgust since the 15th century). No creature alive is stinkier than a skunk. Because "skunk" rhymes with "drunk," the two words are a natural match.

Since skunks do not drink alcohol, "drunk as a skunk" (meaning "extremely inebriated") cannot be pinned on the habits of Mephitis mephitica, the charming North American mammal and member of the weasel family which takes its name from the Algonquian Indian word meaning "urinating fox." The term "drunk as a skunk" is, as you guessed, simply a good example of our love of comparisons and rhyming, made especially popular by the fact that "skunk" happens to be one of the few words that rhymes with "drunk." Similar, albeit non-rhyming, terms for "extremely drunk" have included, over the years, drunk as a fly, a log, a dog, a loon, a poet, a billy goat, a broom, a bat, a badger, a boiled owl, and several dozen more too risqué to list here. Although comparative terms for drunkenness have been popular throughout the history of English, "drunk as a skunk" seems to be a fairly recent (20th century) addition to the canon.

The ability of our friend the skunk to douse its enemies with foul-smelling musk has, however, made "skunk" a slang term of derogation in other senses. "Skunk" has, since the early 19th century, been slang for "a contemptible or untrustworthy person," as in "That little skunk told us to buy Enron stock while he was selling his own." And because the odor of a skunk's musk is strong enough to discourage even the bravest competitor, "to skunk" has, since the 1800s, meant "to emphatically, unequivocally defeat," often used in situations where the losing party or team did not score a single point.

http://www.word-detective.com/032602.html

One theory.. It came about because skunks (and other animals no doubt), while they don't drink alcohol in the literal sense, do eat fermented fruits and berries fallen from trees and as a result become intoxicated. Fruits obviously contain sugars, and there are wild yeast and other bacteria floating around in the air which will ferment these sugars, producing alcohol. Leave a glass of water mixed with sugar sitting around uncovered for a few days and you will notice it bubbling away - it's picked up a wild yeast and is fermenting. :)

Although skunks are classed as carnivores, feeding them red meat results in illness and early death, and is no doubt the reason why they previously died out in this country. Recent studies of the stomachs of wild skunks, shows that they eat large numbers of insects and arachnids, particularly scorpions, along with some roots and fruit. Eating fermenting fruit, fallen from trees, results in them becoming intoxicated in the wild, hence 'Drunk as a skunk'.