The worst ever was when the match fixing scandal broke ofcourse.
But the corollary is more damaging - when you watch re-runs of matches with Sachin's captaincy, there are so many ouch moments, involving the likes of Azhar and jadeja, where you realise that it is not lack of talent but malafide intent that caused them to perform as they did. It just makes any discussion on Sachin's captaincy null and void.