The joke, but more an analogy, about lipstick on a pig or putting lipstick on a pig is an old one. And Google can vouch for this with its search results.
But what is interesting is that in the site Democratic Underground under its General Discussion area, there was a little exchange last September 3rd essentially about the Palin pit-bull/lipstick remark, with one participant claiming that Palin plagiarized the joke from a documentary titled Stumped.
The next participant then titles his comment with: lipstick on a pig is still a pig, with a brief comment: “just saying” and the commenter’s accompanying image on the right is that of Barack Obama.
DU being a very popular liberal site, did the Obama campaign go mining for good talking points or clever punchlines from one of its surrogates, to directly bring down the Palin remark?
Remember in the original context the joke or analogy (lipstick on a pig is still a pig) clearly referenced to the statement of Palin during the RNC convention.
You be the judge.