From Chris Ambidge a few days ago, this reproduction of a Jell-O ad from roughly 50 years ago (now in a color version unearthed by Chris Hansen). Go gay with Jell-O today!
This was from a time before the ‘homosexual’ sense of gay spread into general use, when the relevant sense (from OED3, August 2010) was:
Of persons, their attributes, actions, etc.: light-hearted, carefree; manifesting, characterized by, or disposed to joy and mirth; exuberantly cheerful, merry; sportive.
Now of course we’re inclined to see double entendres in material like this, and people complain that homosexuals have “stolen” the word gay — though in fact all they/we did was introduce another sense of the word (well, really, another word), usually easily distinguishable in context from the one above. Then the usage above was contaminated for people who were offended by the mention of homosexuality.
Here’s another gay Jell-O ad, from the 3/5/45 issue of Life magazine: