static const int ZEN_ADJUSTMENT = 12345; //When I wrote this only myself and God knew what this value meant, now...

  int AddWithAdj(int a, int b) { return a + b + ZEND_ADJUSTMENT; }

And now the maintainer is going to wonder why the originally programmer defined ZEN_ADJUSTMENT just above this function, but actually used ZEND_ADJUSTMENT (which is apparently defined somewhere else in the code). By design or typo!? :-)