Happened to me as a kid. There was some strange guy sitting in there. As he turned around I realized I was in the wrong car and I opened the door and ran back to the other car with my grandpa in it as if I am being hunted by demon hounds.Cars. I pay so little attention to them that the general shape and colour are enough for me to climb inside a stranger's completely unintentionally. Last week it happened when there was a stranger inside at the time.
True story...
I still dream about that sometimes.