@ will-w
you'll have more success if being calm
I think it would be a good idea to show them this photos first; then the actual car
after, ask with a big smile, which car belongs to their director or owner; then pull out of a bag some scrubbing pads and say smiling, you'll return the service by cleaning his car.
When THEY begin yelling, replay, they can call the police and you'll post them on internet and youtube.
I can assure you, the treatment will make them softer