I stumbled upon a humorous blog post about a particularly unusual DA clue.
As is the wont of inferior mortals, the author disparages what he cannot understand.
In the comments, though, a more enlightened reader claimed the following:
I had once read that the hardest ever clue was in The Times (UK) crossword some time way back in the eighties.
Clue: E (13 letters)
Try solving it before reading the comments where the excellent answer and explanation are revealed.