It's a Dilbertism,
isn't it?
(DogHorsewants to do a poo in Paul's bathroom, Tue 3 Aug 2004, 15:57,
archived)
I believe
so
(MakTheYak, Tue 3 Aug 2004, 16:01,
archived)
It predates Dilbert.
It probably originated on talk.bizarre, an old Usenet newsgroup.
(NewingtonHM Time Corps: Quo vadimus non requirimus vias, Tue 3 Aug 2004, 16:13,
archived)