The theory behind this is to entice and motivate guests to take part in the spectacular celebration of your wedding day.  Inform guests in advance and solicit those willing to participate to give them opportune time to practice.  The competition could be a duo or group dance.  Those guests not participating will be the judges and will be given a score card and/or the winners may be determined via the loudest applause.  Also, in advance, consider prize options for the winners to include table center pieces or perhaps a small gift card.  This is a friendly contest designed to infuse fun and stage a unique element into your celebration.