A mass fob occurs when group of people arrange to appear from out of nowhere, to perfom predetermined actions, designed to amuse and confuse surrounding people, much like flash mobbing However unlike flash mobbing the group all decide to fob off the activity in favor of something else.
person 1:We gonna flash mob the high street then?
person 2:I cant be bothered me like.
person 1:I wont go either then.
person 2:If nobody went we would have a mass fob