I will never forgive him for forcing Dayne Crist to be a dink and dunker, not taking advantage of that strong arm (he threw amazing frozen ropes downfield), especially with a developed Michael Floyd in the WR corps.
I still have an eternal anger at Kelly for making him run all of those spread-option QB runs, which led to his knee getting shredded.
I absolutely despise the way he threw Crist under the bus after one bad series, while giving Tommy Rees the kid gloves treatment after a lot of boneheaded throws.