The ass crease of doom
The ass crease of doom (never capitalised due to an error in the Ordnance Survey map) is a rather large dent fashioned by the buttocks of a member of the Automobile Association. It can be found in any AA vehicle that has been in active service for over 70,000 miles. Incidentally, that is also the distance between Usain Bolt's legs after riding a flaming horse.
One can observe this phenomenon (the ass crease, not Bolt) by calling the AA. If you are a member, you can see this spectacle for free. Critics agree that this is the safest, if not cheapest, way.
Prior to 2008, it was known simply as the 'ass crease' but members of the ACAGB (Ass Crease Association of Great Britain) voted to add the 'of doom' bit by a majority of 3-1. The panel was later disbanded after it was found that one member did not, in fact, have an ass, and another no brain to speak of, having undergone an emergency lobotomy in the 1990s.