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.
Dude that guy on the corner wears a tinfoil hat and ripped all the wires out of his house so the government couldn't listen to his thoughts.

Really?

Yeah, he's batshit crazy.
by KBLI August 20, 2009
adj. speech or behavior that is over the top, unhinged, self-destructive, or a threat to others.

Condition may be temporary (e.g. "Dad went all batshit crazy on me when he saw the cell phone bill") or prolonged ("Adolph Hitler was a batshit crazy megalomaniac responsible for the deaths of millions in 20th-century Europe.")

see batshit, batshit fucking insane
Did you see what Maureen wrote last week? Girl's been batshit crazy ever since Michael dumped her.
by Jim Wright August 9, 2006
Bryndon Fisher expects to received $125 a share for his fannie mae & freddie mac common shares from the US government. This is batshit crazy.
by Fanniegate April 21, 2022
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.
crazy: throw a brick through your window

batshit crazy: throw a brick through your window, call the cops, wait for them to arrive, tell them what they did, and still get away.
by maximushyrule June 16, 2008
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.
Bill wants to buy an Oz of green for 20 bucks, yea that bill he's batshit crazy
by bs425 December 26, 2014
Sarah Palin, just delivered a speech supporting Donald Trump that made absolutely no sense, that bitch is batshit crazy!
by Redbitchbetty January 21, 2016