According to the pilot, he was landing after a local flight with a passenger seated in the rear seat of the tail-wheel equipped airplane. During touchdown the airplane started to nose over, and the pilot realized that the passenger had his feet on the brakes. He yelled at the passenger to get his feet off the brakes, but it was too late to prevent the airplane from nosing over. The airplane flipped over inverted and came to a complete stop. Examination of the airplane by a Federal Aviation Administration inspector revealed that the vertical stabilizer was buckled. The pilot reported that there were no preimpact mechanical malfunctions or failures with the airplane that would have precluded normal operation.