don't crap where you eat
Do not engage in troublesome or dubious behavior at one's home, place of business, or any location where one frequents, for it invites undesired consequences. (A more offensive term is often used instead of "crap.") I warned him—I told him, "Don't crap where you eat." But he still insisted on having an affair with his secretary, and now, the scandal is ruining both his professional life and his home life.