I would say, my favorite scenario would be the one where they're forced to wait right outside the bathroom. So close to relief, but having to wait for a few more minutes while someone else gets their's making it that much harder for them to hold it.
That's an interesting though to have. I suppose that not needing to poop or pee would be extremely convenient to just about everyone. I guess as long as water stay readily available we can always indulge in our desires.