(Originally published on Fimfiction)
Don’t get me wrong, you can do a lot of fun stuff with horsecock. It’s the word “horsecock” I have a problem with.
Let me ask you this: If you were writing a story that takes place in our human world, would you call someone’s dick a “humancock”? Probably not. In our human world, a “humancock” is just a cock.
The same idea applies in a world filled with horses: A “horsecock” is just a cock.
There is only one place I can imagine “horsecock” being legitimate: a story that involves someone “bringing” a horsecock from Equestria into the human world of Equestria Girls. In this case, a horsecock isn’t the norm in the human world, so it’s fine to use that term.
Another place that you might argue for is in an anthro story, where the form of the penis could be either equine or human. But I’d favor just describing the penis and letting the reader figure it out.