Shit or get off the pot.
The informant says she learned the above proverb from her mother, probably as far back as childhood. The proverb is typically used to express frustration over somebody not getting something done. The informant believes that the saying is useful in that its to the point: either produce or move on, enough is enough.
Like the informant, I found this proverb to be a useful way of communicating ones frustration with another person. The vulgarity seems to ensure that the saying is likely to be directed at somebody who is relatively close to the person uttering it, as well as that the line will quickly catch the attention of its recipient. The slang, or perhaps, antiquated term pot, clearly referring to a toilet bowl, is similarly rugged and catchy. Unlike the informant, I think that the above proverb may connote not only frustration that someone is failing to produce, but perhaps that they are doing so in an untimely manner, and/or that they are impeding someone else (most probably the person using the proverb) from performing the same activity. This interpretation and use seems more specific to the metaphorical language of the proverb, which appears to invoke the image of someone unable to go to the bathroom on account of another taking his/her time in carrying-out the intended action of the other.