At some point, you've probably thought to yourself "I'd love to write some code, but the keywords in my language of choice are just so pedestrian." Your vocabulary is more embiggoned than that of your colleagues. While they're content with DROPping a database object, you'd prefer to efface it. A contractor that Charles I.'s worked with was one of these elite.
His first order of business? Get rid of those (ugh) "while" loops that his mouth-breathing coworkers used. With the belief that elegant code should embody every aspect of the word "elegant," he wrote all of his "while" loops as "whilst" loops.
The day before his contract expired, he checked in all of his changes. And needless to say, it wouldn't compile anymore.
"The problem has to be on your end," he insisted. "It works on my system." For good measure, he compiled it and demonstrated that it worked.
Charles did the sensible thing — a find/replace to change all "whilst"s to "while"s, rebuilt, and everything was fine. Still, it was odd that it worked on the contractor's computer. A few months later, they figured out why:
#define whilst while
The compiler they used had a common header file that it'd include in each compilation. The file is in the local installation directory, and just specifies directives and things to configure the compiler. The only person who knew about the file was the clever contractor.