I've had exactly th same problem with our Chitty...
On Fathers Day, the girls (then 3.5yrs and 1.5yrs) and I drove up to our high street to get my father a card.
Since it was really early everything was closed, except for McDonalds, so we parked up outside next to a window and I had a coffee.
Loads of people stopped and looked as they walked by, some kids beeped the horn, which is fine.
But then an older chap, must have been 60 or so, started poking at it. He wiggled the windscreen a bit, then bent it over, bending the brass brackets and walked off!
Why?
I don't get it.
What is wrong with people?
I don't mind children playing with it; if they're having a look I quite often tell their parents' they can climb in and beep the horn etc (but not drive it)... But some children climb in straight away. My little'un gets really quite possessive about it, its quite funny watching a 2 year old storming across the playground shouting 'My Chitty, my chitty'.
Soceity today, huh, tsk!