One who takes advantage of the ambulance moving down the highway - disrupting other vehicles from merging back into traffic. Basically, an ambulass follows the ambulance through traffic - cutting off all motorists along the way. An amubulass usually drives an SUV or Hummer.
Traffic is heavy on the highway. An ambulance is approaching so all vehicles move to the left or right lane and stop. The ambulance moves through the middle lane. As vehicles begin to merge back into the middle lane, they are suddenly cut-off by an ambulass following the ambulance at 40 mph - the ambulass takes advantage of the wake caused by the ambulance - and damn near wrecks into several cars along his chase.