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von Windfall (GB), 2013-11-18, 11:32   Spam?  

Unless I'm missing something, I think you're right that it's a joke for not being a joke.

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von Lllama (GB/AT), 2013-11-18, 11:37   Spam?  

http://www.zimbio.com/TV+Recaps/articles/7CoYAUSaj6z/Vampire+Diarie...
Is Silas(?) just announcing to everyone that he's killed the mayor or did they know already? I assume the former and that's supposed to be the joke: rather than just saying, "I killed the mayor", he's made it into a joke.

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von Windfall (GB), 2013-11-18, 11:44   Spam?  

Interestingly, my first assumption was also that it came from fiction and was being said by someone who had just killed the mayor. I think the Joker may have made a similar joke in one of the Batman movies.

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von Lllama (GB/AT), 2013-11-18, 11:51   Spam?  

Google just brought up entries about Vampire Diaries.

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von gatv (UN), Last modified: 2013-11-18, 11:58   Spam?  

thanks everybody,
yeah it's Silas from the Vampire Diaries
4; Lllama: You might be right (I just don't remember if everybody knew already or not)

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von Windfall (GB), Last modified: 2013-11-18, 13:44   Spam?  

The Batman thing doesn't Google well at all, but I know I haven't seen the Vampire Diaries, so now I'm not sure if I just recognised this as the type of thing you find in fiction (and my brain filled in Batman as a likely vehicle for this sort of joke) or whether it really was in one of the many Batman films/TV show episodes I have seen. Not that it much matters either way.

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von Catesse (AU), 2013-11-18, 13:44   Spam?  

"Knock, knock" is a children's word game that was ancient even when I was a tiddler.
See: http://www.funology.com/knock-knock-jokes/
Or just google "knock knock jokes".
That being said, the joke quoted by gatv is a fairly poor specimen, as it departs from the original concept.