THE PILOT WAS DEMONSTRATING A GLIDER TAKEOFF TO THE PASSENGER. THERE WAS CONFUSION ABOUT WHO WAS ACTUALLY ON THE CONTROLS FOR TAKEOFF, THE PILOT OR THE PASSENGER. THE WIND WAS A QUARTERING LEFT TAILWIND AT 13 KNOTS WITH GUSTS TO 17 KNOTS. DURING THE GROUND RUN, THE RIGHT WING DRAGGED ON THE GROUND AND DIRECTIONAL CONTROL WAS LOST. THE PILOT IN COMMAND TRIED TO REGAIN CONTROL, BUT THE WING STRUCK A PARKED VEHICLE AND A BUILDING.