It's wrong to poop in public.
Nancy is a homeless drunk wandering the streets of San Franciso.
Nancy needs to relieve herself.
Nancy goes into a nearby Starbucks to use the restroom because they allow non-customers to use their facilities.
Nancy squats on the sidewalk and defecates on it, in front of several passers-by.
Nancy is able to relieve her bodily functions in a clear and appropriate place.
Nancy is arrested for public lewdness and taken to the police station.