code: public void setUnacceptable(E element) {
  
      Ranking ranking = this.map.get(element);
      if (ranking == null) {
        ranking = new Ranking();
        this.map.put(element, ranking);
      }
      ranking.setUnacceptable();
    }
docs: This method ranks the given {@code element} as {@link #RANK_UNACCEPTABLE unacceptable}. After the call of this
  method the {@link #getRank(Object) rank} of the given {@code element} is set to {@link #RANK_UNACCEPTABLE} and can
  NOT be changed again.
  
  @param element is the unacceptable element.