As defined by dictionary.com:
Main Entry: McGuffin
Part of Speech: noun
Definition: in film, a plot device that has no specific meaning or purpose other than to advance the story; any situation that motivates the action of a film either artificially or substantively; also written MacGuffin
Etymology: Alfred Hitchcock’s term, based on a story where this device was used in a story set on a Scottish train
(As seen in this Firefly-virgin’s review of Serenity).

…see here: apparently, you can go to jail if you post something “annoying” on the internet.
Update: There’s a followup article, with some Q&A, here.