This came up on The Consumerist today. Apparently, people who ran multiple strings of Christmas lights were running some of the strings backwards. Instead of re-running them, there were coming in and asking for double male edison (as we call them in show business) plug adapters! And an Ace Hardware store made a sign to discourage people from asking about them:
This is probably more scary than the infamous J-CON 1/4" to edison adaptors pitched at an AES convention as a speaker cable solution!