‘Planking’ is the latest fad to sweep through facebook.  It involves laying someone down on their belly in a dangerous position and then taking a picture that is placed on Facebook. 
Read more here: Facebook ‘Planking’ Craze Under Fire In Australia http://therandomforest.com/facebook-planking-craze-under-fire-in-australia/#ixzz1M9YiEADr

And here are 10 other fads that have swept through Facebook:  http://www.telegraph.co.uk/technology/facebook/8509708/Planking-Top-10-Facebook-crazes.html