How would that conversation go, exactly?
something like this:
***DING DONG!***
hi! i was in the neighborhood and thought i'd drop by for a visit. direct me to your facilities, please!
i was thinking along the lines of a friend or acquaintance stopping by under the ruse of some legitimate purpose only because i was nearest to them at the time nature called and they were too ashamed to use a public toilet.
no one has actually done this to me, but justsomeguy's experience made me consider that someone could have the audacity to shit and run... and that's just rude.