The phrase comes from the Happy Days episode when Fonzie jumps a shark on water skis. So I think of the phrase as meaning a more specific point in time, whether that's accurate or not.
For me, if there is a single moment where I kind of am set aback, it would be the final episode - season 12, episode 19 - Woe to Wo Fat. Why? For me - it's McGarrett's disguise, plain and simple. I just felt that was beneath our beloved McGarrett character and was just too much - I thought the disguise was kind of foolish and was just sort of a desperate reach.