Football is the obvious one. I'm being treated to expert opinions from people who don't have any real interest in the game but actually think they know more than Fabio Capello.
My usual favourite however is Mossad/SAS/Special forces. Someone dies overseas in fairly shady circumstances and suddenly people who have never left their postcode, have no idea about the inner workings of state security and are just a bit of a melt are informing everyone that it simply must be a Mossad operation, as it has all the hallmarks of one.
File under 'threads that sounded better in my head' 255 of 500