Given Donald Knuth's legendary sense of humor, one cannot help but suppose he would have succumbed to the temptation to add in a "special" command or two that did something unsuspected or unusual just for the fun of it. (And I don't just mean some cute or funny source code comments, but something that actually does something.)
And if not him, then surely someone in the community who has made an extension, document class, package or subversion of TeX, LaTeX, ConTeXt, or a helper program like an editor, etc., decided to have a little fun and throw in an Easter Egg.
Yet, at the moment, I cannot think of a single one. Does anyone know of any?