The pilot and the pilot-rated passenger planned to conduct a personal flight in the tailwheel-equipped airplane. The pilot was in the rear seat, and the passenger was in the front seat. The passenger did not have a tailwheel endorsement, but he planned to follow the pilot on the controls during the takeoff for familiarization purposes. During the takeoff roll when the airplane was approaching liftoff speed, the airplane made a rapid veeroff to the left. At that point, the pilot abandoned the takeoff, and made the conscious decision not to attempt to return to the runway, instead allowing the airplane to roll and decelerate on the grass/gravel beside the runway. That decision was based on the pilot's desire to avoid any potentially hazardous maneuvering or a ground loop. During the rollout, due to the pilot's inability to see directly ahead, the airplane struck the VASI (visual approach slope indicator) installation located about 1,300 feet down the runway, and offset about 145 feet from the runway centerline. The airplane sustained substantial damage to the left wing struts. The pilot stated that he did not believe that any mechanical malfunction or failure contributed to or caused the runway excursion, and that he could not rule out the possibility that he had inadvertently applied one wheel brake during the takeoff roll.