Baumgartner springs to mind - his first run his racing lines to each corner made it look like he was not ready for F1 and Brundle in the commentary was critical of him
Basically over two threads, it would seem every single world champion is overrated and any driver who drove for a back marker and was just a bang average driver could be classified as being the worst.
I was actually hoping, between the overrated, underrated and worst driver threads, instead of naming every single F1 driver who ever jumped behind the wheel from 1950 until the present day, people would actually pick one and put up a case as to why that would be the person to fit that criteria.
While I guess many drivers could be considered over or underrated, in the worst driver thread the clue is in the title.
There can only be one, the most, the utterly, absolutely worst driver who actually attempted to have an F1 career rather than rock up for a race or two.