A person who is batshit crazy is certifiably nuts. The phrase has origins in the old fashioned term "bats in the belfry." Old churches had a structure at the top called a belfry, which housed the bells. Bats are extremely sensitive to sound and would never inhabit a belfry of an active church where the bell was rung frequently. Occasionally, when a church was abandoned and many years passed without the bell being rung, bats would eventually come and inhabit the belfry. So, when somebody said that an individual had "bats in the belfry" it meant that there was "nothing going on upstairs" (as in that person's brain). To be BATSHIT CRAZY is to take this even a step further. A person who is batshit crazy is so nuts that not only is their belfry full of bats, but so many bats have been there for so long that the belfry is coated in batshit. Hence, the craziest of crazy people are BATSHIT CRAZY.

1. A synonym for Tom Cruise.

Originated by observing the way bats defecate. Bats hang upside-down and poo upside-down. If people were to hang upside-down and poo it would go all over their face therefore only a crazy person would shit like a bat making them batshit crazy.

someone who has absolutely nothing to lose. batshit crazy people are different from regular crazy people because of their attitude and activities. a regular crazy person would shoot at a plane with a pistol. a batshit crazy person will jump off of one plane with a knife in their hands, onto another, break the glass and kill the pilot ... and land safely. in order to be truly batshit crazy the person must do the most outrageous things every and still return safely.

Sarah Palin!

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.