In the Isaac Asimov Super Quiz from 2/7/2005:
I thought I knew a something about waterloo, butt I have never heard anything about this. Anyone know the story behind this. Something about it doesn’t sit right with me. In case there’s a test I want to have made preparations…
Dis Colon Rectum. 1988 Apr;31(4):303-5.
Piles of defeat. Napoleon at Waterloo.
Welling DR, Wolff BG, Dozois RR.
Section of Colon and Rectal Surgery, Mayo Clinic, Rochester, Minnesota 55905.
Major events of history have frequently turned on seemingly trivial matters. One such situation involves Napoleon Bonaparte at Waterloo. Napoleon was not feeling well on the day of the battle of Waterloo, despite fighting well at Ligny, a few days before the last, dramatic June 18 battle. There is considerable indication that Napoleon was bothered by very painful thrombosed hemorrhoids. Did this affect his generalship that day? What is the evidence that Napoleon was afflicted with thrombosed hemorrhoids? What contribution could this factor have made to the French defeat at Waterloo?
I can’t find the full article online, but that’s the story in a nutshell.
Well, the French (not necessarily Napoleon in particular) screwed up badly several times over the course of the day, and some apologists for Napoleon’s unsurpassed military genius 
seize on whatever they can to provide an explanation for why it wasn’t Napoleon’s fault. I’m not sure why, exactly.
That’s punny!