Me, one of my stock favorite poo-phemism is “business,” as in, I’ve got “the business.” The beauty of business is that it can spawn so many derivations, as in “I have to take a business meeting” etc. The bathroom becomes the boardroom, occasionally one might have to “liquidate some assets” and on and on.
See, it’s fun! Play along at home. See how many poo-phemisms you can come up with!