This
farewell is a truncated version of the expression "It's been real,
it's been fun. Just hasn't been real fun!" It is not necessarily a
slight to the person you are leaving, but more of the situation or experience that you have just shared.
While being
dropped off after a
car ride with a friend during which you helped him change a flat tire and
ran out of gas - you turn to him and say"It's been real!"