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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 19, 2009
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2
A clinically insane person beyond the regular diagnosis given to them by a psychiatrist.
Family: "So, did he have a psychotic break? Or is he manic/depressive?"
Doctor: "No. I'm sorry. Your son is bat shit crazy."
by Brainiac March 02, 2005
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3
Acting in a generally insane manner; Tom Cruise.
When Tom Cruise jumped on Oprah's couch, he proved he was bat-shit crazy.
by Lorraine Bates July 30, 2006
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4
adj. (slang): A combined state of mental agitation and physical volatility. It's use may provide warning that the individual it describes has lost all self-control and cannot be reasoned with. Can refer to either a chronic or temporary condition.
I wouldn't go in there if I were you, Dolores is bat-shit crazy .

by maximo hudson January 19, 2009
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5
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 25, 2014
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6
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 08, 2006
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7
Tom Cruise is batshit crazy.
by Robert O'Fredreck-Llewellyn March 02, 2008
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