From China Digital Space

狂草泥马 (kuáng cǎo ní mǎ): crazy grass-mud horse

In the fictional grass-mud horse eco-system, the crazy grass-mud horses reign over the regular grass mud horses. In Chinese 狂 (kuáng) means "crazily", "violently" or "insanely," thus in Chinese 狂草泥马 sounds the same as crazily/violently/insanely f**k your mother.