"SOMETHING_ELSE" isn't all upper case. I also think best practices indicate that you should avoid all-lower-case subroutine names because conflicts there are even more likely (unless you prefix your subroutine calls with &, something that likely gets you yelled at, usually for silly reasons such as "looks like Perl 4").

If you can't think of a multi-word name for your constants, you could go with a Hungarian-ish lower-case prefix like "cDEBUG", as "DEBUG" certainly seems like something a future version of Perl might make use of. (: