Don your best choker. Pull on your denim overalls. Put down Pokemon Go for a minute, and switch Gilmore Girls off the TV, because 2016 was a 90's nostalgia fest. From Full House, to the Spice Girls reunion, why are we suddenly craving the delights of the nineties? It's psychology, of course, and social media. But enjoy it while it lasts because there's a theory that mass nostalgia, the way we've seen it emerge this year, will never happen again.