What is the worst real-world macros/pre-processor abuse you've ever come across?

What is the worst real-world macros/pre-processor abuse you've ever come across?

c++ c macros preprocessor

c

How to convert an enum type variable to a string?

c++ c preprocessor ansi-c

c

Can gcc output C code after preprocessing?

c c-preprocessor preprocessor preprocessor-directive

c

I need a way in a C preprocessor #if to test if a value will create a 0-size array

c preprocessor

c

Is there a C pre-processor which eliminates #ifdef blocks based on values defined/undefined?

c++ c preprocessor

c

Can I add numbers with the C/C++ preprocessor?

c++ c metaprogramming preprocessor

c

Why other languages don't support something similar to preprocessor directives like C and its descendant?

c programming-languages preprocessor

c