In common usage the KC Metaphor is simply to do with the futility of turning back tides; he is cast as Graves' Caligula in this respect, waging war with Neptune. Maybe the historical Caligula was like that too. I confess, many mistaken Common Usages do irk me - Green Men for one / Ring a Roses for another - but both of these I fear are the consequence of Folkloric Wonkiness finding its way into the mainstream rather than any feral-thang in and of itself. The Common KC Metaphor (however so mistaken) is totally feral; the others are just bad folkloric-factoids gone awry.