The adjective 'batshit' (almost invariably premodifying the noun 'crazy') derives from the fact that the
guano of certain bat species, when smoked, vaporises as a potently psychotropic narcotic. The word entered the popular consciousness after one of several dozen guano collectors dropped his torch, igniting the batshit (which, as a
fertiliser, is flammable)
swathing every surrounding surface. The fire spread rapidly, but all the workers managed to flee in time - having, however, inhaled a considerable quantity of the smoke. The resulting deranged rampage made the international news, and "
bat-shit crazy" was used in the New York Times headline. This coinage by the relevant subeditor
seeded the general currency of the term, consolidated by a brief outbreak of the use of guano as a recreational drug, before even the most hardcore druggies concluded that it was just too batshit crazy.