I heard that "comeback" growing up. What I didn't know, was apparently, it originated in the Bible. In Isaiah 36:12. When the Bible speaks of something it's not necessarily approving of it. Sometimes it's clear that the Bible disapproves of something -- when it begins with "though shalt not ..." for instance. But, Lot's incest with his daughters? All of those polygamous characters? I'm not sure that the proper way to interpret these passages is that the Bible speaks approvingly of these things.
Likewise with Isaiah 36:12, I'm not an expert on the context. But, apparently, it's the Bible telling some folks off with an "eat shit and die, man."
From the King James:
But Rabshakeh said, Hath my master sent me to thy master and to thee to speak these words? [hath he] not [sent me] to the men that sit upon the wall, that they may eat their own dung, and drink their own piss with you?