Everett Howe, Hendrik Lenstra, and David Moulton: My butter, garçon…, p. 28 in: A. van der Poorten, Notes on Fermat's Last Theorem, John Wiley and Sons, New York 1996.
Reprinted (without permission, mind you, and with a misspelling and some altered punctuation and typography) on p. 306 of: S. Singh, Fermat's Last Theorem: The Story of a Riddle that Confounded the World's Greatest Minds for 358 Years, Fourth Estate Ltd., London 1997. Singh's book has been reprinted in the United States by Walker & Co. under the title Fermat's Enigma: The Quest to Solve the World's Greatest Mathematical Problem, and the American editors corrected the misspelling that the British typesetters added to our work.
This work is the only item referred to in this bibliography that is shorter than its bibliographic entry. But I'm not going to quote it for you — you'll have to look it up. It might help if you go to Google and search for "worst limerick in the world".
Update: The top hit of the google search I just described used to lead to a page with our limerick, but now that page has disappeared. You can still find it here on the Wayback Machine.