"Parbleu," said Poirot. "At this moment I am feeling that I am considerably further back. I seem to progress en reculant."
"That's bad. But I don't really believe it, M. Poirot. I've been hearing all about you and what a wonderful chap you are. Never had a failure, they say."
"That is not true," said Poirot. "I had a bad failure in Belgium in 1893. You recollect, Hastings? I recounted it to you. The affair of the box of chocolates."
"I remember," I said. And I smiled, for at the time that Poirot told me that tale, he had instructed me to say "chocolate box" to him if ever I should fancy he was growing conceited! He was then bitterly offended when I used the magical words only a minute and a quarter later.
(Peril At End House by Agatha Christie, Chapter 15)