I think it would help if you explain the context a bit more. “Don’t shit where you eat” usually refers to avoiding romantic endeavors at work, but if that is the context you’re talking about then I’m not sure I understand why you’re rejecting “don’t dip your pen in the company ink” as having a different connotation.
“You watch Mad Men? Well, don’t do what they do.”
He that troubleth his own house shall inherit the wind.
Don’t rock the boat, especially if you’re in it?
Do Not Taunt Happy Fun Ball?
I’m not the OP, but I’ve always taken the first to have a far broader meaning than the later. Dipping your pen in company ink has an almost exclusively sexual connotations. Where as shitting where you eat, can include any non work activity including 3 hour martini lunches, e-bay, facebook (much of the internet really), or anything else other than what you are supposed to be doing.
Concur. The most straightforward equivalent to “don’t shit where you eat” I know of is the aforementioned “don’t mix business with pleasure.” But because different people have different associations with even that fairly innocuous phrase, I too was hoping to get a better sense from the OP of what they meant to warn against in literal terms.
Don’t excrete fecal matter where you ingest nutritions
I guess I just hear it used as a sort of generic, catch-all “avoid all conflicts of interest” warning, whether they’re personal, sexual, professional, whatever - just as a sort of tough-guy way of pointing out a potential conflict of interest that someone may be heading into.
Don’t tug on Superman’s cape?
Don’t spit into the wind?
Don’t pull the mask off an old Lone Ranger?
Don’t mess around with Jim?