Entertainment media's driven a lot of it, I think, for whatever reason. Generations X and Y have tended to make catching accidental (and not even especially interesting) double entendres a prominent feature of the humor-media they've (we've) created in a way it wasn't (yes, some, but not so constantly) before. Earliest example I can think of that did a lot of this is Beavis & Butthead, but it's been all over the place since then. I'm not sure reduced formality's behind the presence of so much of that in media, all of the sudden.