This phrase means "do not have romantic relationships with any co-workers." Basically, you don't want to make yourself uncomfortable (by potentially having a romantic relationship get ugly, or "shitting") at the place where you work ("where you eat").
Dude #1: "damn a really hot blonde just started working at my company. i'm gonna ask her out"
Dude #2: "dude, haven't you heard the saying: Don't shit where you eat?"
a phrase meaning, there's no point in arguing with you because you adamantly believe in a scientific fallacy- something that has been scientifically/socially proven to be false
Sometimes you eat the bear ... and sometimes the bear eats you. Expression describing the bipolar nature of life, the universe and everything, popularised among other places in the movie The Big Lebowski and fifty percent proven, at any rate, by the life of Timothy Treadwell.
Well, dude, sometimes you eat the bear, sometimes the bear eats you. But why d'ya have to use so many cuss words along they way?
This expression refers to doing anything that would jeopardize something important or essential to you. A common example of shitting where one eats is engaging in a romantic affair with a co-worker, but lying to your roommate or stealing from friends also fits this expression.
Local Bike Shop Mechanic #1: "Can you believe that guy? I've hooked him up dozens of times, but after the tantrum he just threw, I'll never take a dime off a part for him again."
LBS Mechanic #2: "Seriously. Hasn't he ever heard? Don't shit where you eat."