I think you have to go beyond just being a bad head coach and add some sleaze, fraud, or huckesterism. A lot of the leading candidates here got mentioned. I think Charlie Weiss and his decided schematic advantage is more of a blowhard. Fran's newsletter takes him into rare air. George O'Leary and his resume lying is a pretty solid choice. How about:
Tommy Tubberville: TT got a long way with his church of Christ image and folksy homespun assurances. He was not a bad coach at Ole Miss, but remember his "pine box" statement and then lightning departure to Auburn? On the Plains he does good job, but Auburn goes full Auburn after a losing season and he packs his bags for Tech. In Lubbock, he proceeds to run what had been a pretty decent Big XII program straight into the ground. Tech is still happy to give him some more time, but he actually leaves two recruits in the middle of dinner and disappears to Cincinnati, a place he also left worse off than when he found it. Also, he was sued for managing a hedge fund that defrauded investors. His co-defendant was found guilty and he settled for an undisclosed amount.