I saw a post today that featured the joke about curtains matching drapes, referring to head hair color matching pubic hair color. I imagine that most Americans know exactly what this means, and it got me wondering how things spread so widely before the Internet.
I imagine a lot of sayings like this got started in media, and people found it funny and started using it, but without the Internet to unite the humor of the county I'm surprised this kind of thing had any staying power.
As long as we've had speech, we've shared jokes, memes, and idioms. It's kind of part of how communication/culture works. You might find a fuller answer to this in /r/linguistics or /r/sociology.
There's a professor, Alan Dundes, who studied the spread of jokes and tales. Before modern technology, they were spread by word of mouth, and got quite far that way. Later, they were spread by passing papers, and faxing, and finally by the internet. He describes transmission of these things in: Urban Folklore from the Paperwork Empire and its sequels: When You're Up to Your Ass in Alligators, Why Don't Sheep Shrink When it Rains, Sometimes the Dragon Wins, and Never Try to Teach a Pig to Sing