I don't think you can put someone in the "worst ever" category without bankruptcy. There has been a lot of very shitty CEOs over the years, some of them criminal.
Bankruptcy and criminality? Enron[1] comes to mind.
Kenneth Lay[2], the founder and final CEO of Enron, was convicted of multiple counts of conspiracy and fraud, and would have been one of the few CEOs to have actually been sent to prison. However, he died before the judge had the chance to sentence him. Enron, of course, suffered bankruptcy.
Jeffrey Skilling[3], who stepped down as CEO of Enron (to be replaced by Lay), is currently serving a lengthy prison term.
HP may have suffered under Fiorina, but at least they're still alive.
