h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

When at school a friend told me the story of a couple, known to his cousin, who went on a driving holiday through France stopping at various places along the way.
One night whilst driving through some woods the man stopped the car in a lay-by to relieve himself. He informed his girlfriend that he would not be long and disappeared behind a tree. Time passed and the girl began to wonder why her boyfriend was taking so long. She looked around but could see nothing. She opened the car window and shouted to him but there was no reply. She began to feel a little apprehensive and closed the window. She was just about to open the car door when she heard a single thump on the car roof. This scared her and she quickly locked the doors. She looked around out of all the windows but could see nothing. She then heard a steady soft thumping noise on the roof. She thought that it might be her boyfriend trying to scare her but it was not like him to do such a thing and she was too scared to check.
At that point a car passed and slowed down beside her. She was about to wind down the window to call for help when the car sped off at high speed.
Again she heard the thumping noise on the roof, now getting slightly harder. A police car now pulled up some way from their car and using a loudhailer spoke to the girl. The police instructed her in broken English to open the car door, get out quickly and walk towards them without looking back.
She did as instructed and was almost at the police car when she was overcome by curiosity and looked back over her shoulder towards the car.
What she saw was a man crouched on their car roof with a wide smile on his face. He was gently banging the car roof with a wooden stake with her boyfriends head impaled on the end of it.
The murderer had escaped from a local mental institution. The car that passed earlier had seen him and called the police who were actually searching the area for him. The girl is unable to get into a car to this day.

Excellent story...this legend will be included in the final piece.

I actually believed this one when I heard it and told it to many other people. Only when I heard it again in another form many years later did I realise it was an urban legend. I was very disappointed.