When I saw the biker the first time, I was impressed by the classic Harley Knucklehead he rode. But as I saw him again and again, I began to realize there was something unusual about him. Not just his unusual bike, something more, something not right. I had to chase him down, figure out what it was. It was driving me crazy. Too late I realized, I should have left well enough alone. Knucklehead: Noun, A Harley Davidson motorcycle engine (or motorcycle) manufactured from 1937 to 1947. So named because of the distinctive shape of the cylinder head covers. Adjective, a stupid person, a dumbell. Often will continue a course of action long after it becomes apparent that the course is self-destructive.