# the devil killed you! We couldn’t connect to the db!
if ($res == -666) {
[...]

Source: Direct link to the source code
Software: perl-dbix-ha
Programming language: Perl

/**
 * NOTE! This is very dirty and dangerous trick. I spend
 * several hours on thinking and man pages browsing,
 * but couldn’t find better solution.
 * I know that I will spend 666 years in the Computer Hell
 * for writing this hack, and the master devil (Billy Boy)
 * will send me to write Windowz software.
 */

Source: Direct link to the source code
Software: GNUstep Base Library
Programming language: C++