I guess I'm not seeing the special category that an anime cat girl sits in. Is there some kind of sex implication I'm just not aware of? Linux has a penguin, FreeBSD has a devil(!), OpenBSD has a blowfish, Go has the weird Gopher thing, Gnome has a foot...

Wikipedia suggests that there's an association with queer and trans youth, is that what's meant to make the cock-and-balls comparison work? But it also says it has a history back to 17th century Japan...