How big of a jerk am I? Or are you?

I'm at a complete loss here? You agreed to let someone use your property on the one circumstance that they don't touch your car whatsoever in any way shape or form nobody.
Honestly I don't care if it was a mound of dirt! You gave an intelligent adult clear instructions. I just don't understand how this could have happened.
I don't think anybody should lean on anybody's car for any reason unless it's their own or they've asked.