An alias for POSIXLY_CORRECT. See Democracy Triumphs in Disk Units.

[crb@jane]: ~$ df
Filesystem           1k-blocks      Used Available Use% Mounted on
/dev/hda3             18690576   3958640  13782496  23% /
[crb@jane]: ~$ export POSIX_ME_HARDER=yes
[crb@jane]: ~$ df
Filesystem           1k-blocks      Used Available Use% Mounted on
/dev/hda3             18690576   3958640  13782496  23% /
[crb@jane]: ~$ export POSIXLY_CORRECT=yes
[crb@jane]: ~$ df
Filesystem          512-blocks      Used Available Use% Mounted on
/dev/hda3             37381152   7917280  27564992  23% /

So it's not a very good one, but it's part of the history. :)