The idiom "Fish and visitors stink after three days" is defined as an old truism that comes from founding father Benjamin Franklin, who penned it for his Poor Richard’s Almanack.
The idea is that fish start smelling if they’re left to sit around for awhile, and that visitors, who keep prolonging a visit, can get to be really annoying, fast.
(idiom)An example of "Fish and visitors stink after three days" is when visitors come to stay overnight, but end up spending two weeks.