It would appear from what has been said that the Prius can cope well with abuse, and generally won't do the wrong thing when asked, like go into reverse at 70mph (I know someone who achieved this in a manual, and reduced his vans gearbox to iron filings). However the classic error of drivers coming from manual to autos happens as you slow down after a long steady speed run, when you wouldn't have been gearchanging in a manual. As you lift off the throttle the brain reverts to autopilot, some try to change down, and some try to select neutral. In most cases this also requires a declutch, and so the left foot stamps on the clutch. As there is no clutch pedal this foot normally finds the brake pedal in an auto and results in a thunderstop. I have done it many times as I have had a mix of manuals and autos. In all cases it was my error, not the cars. Even recently though when I had to emergency stop I tried to declutch at the same time. BSM trained this into me 30 years ago, and it would appear the reflex is still there. Chrispy, for your own peace of mind, you need to get your friend to understand this is what probably happened. Then they can get on with understanding these reflexes are simply trained in, and they needn't be embarrassed about it, and you can get on with trusting your car to do what it's told.