In case you're interested in significant historical relics, note that Semi::Semicolons qualifies,
as one of the earliest CPAN joke modules ever released, so early in fact that it
was released before the CPAN Acme namespace was created in 2001 to protect developers
from naively deploying CPAN joke modules in production systems
(though it still happens occasionally).
Acme::Bleach, as the first module in the Acme namespace, also qualifies.
Update: Sadly, the primary author of Semi::Semicolons, David H Adler Esq, passed away recently --
its other authors are listed here.
More detail on the history of the lighter side of Perl culture can be found at: