Not sure of the exact reason behind it, but its amusing enough. Group of people got a load of t-shirts printed up with Half-Price Sale and headed in to linger around major shops. More on the SpaceJackers site

“I have been informed by the manager that you are all allowed to stay in the store, however you must remove your t-shirts”
As we walked off to our next target we were given a round of applause from the Apple staff.