Didn't happen to me but I watched it happen today and was wondering. A 4 year-old opened her door into the car beside it and dinged it pretty good. The mom and the driver of the dinged car swapped contact #'s per insurance. The thing is, the car that got dinged was angled in such a way so that the back tire was actually in the spot taken up by the car with the little girl. So, if you can imagine the front 2 tires of the dinged car entirely within the parking space and the back of the car actually taking up room in the space next to it, you'll get an idea as to what I am talking about.
I spoke to the mother of the little girl and gave her my contact info just in case but I figured someone on here would know the liability.