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01: A mentally unstable person who acts carelessly; 5150.
02: A person who is not of sound mind.
03: A crazy, nutty, eccentric person.
That BTK dude is a real head case.
by Mr. Terrence L. Trezvant March 03, 2005
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Oct 3 Word of the Day
I couldn’t care less (but one must keep up appearances, right?)
Frenemy has a family tragedy. "Thoughts and prayers."
by November 05, 2018
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(noun 1)
a mentally unstable person who acts irrationally or foolishly; an eccentric person

"They put him in a mental institution because he was a headcase."
by Billy Casper March 21, 2008
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A person that is impossible to date due to numerous psychological disorders, offensive personality traits, or unresolved psychosocial trauma.
When we first started dating, I was able to deal with his extreme passivity, unwillingness to drive at night, never wanting to have sex, fear of adhesive tape, and never answering questions about his personal life. I finally dumped that headcase when I found out his current roommate is his ex and they still have freaky bondage sex together.
by DrPotz July 17, 2010
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a colloquial term used to describe a mentally sound person who likes to act foolishly for fun.
"He was being a headcase again."
by Billy Casper March 21, 2008
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A crazy, insecure, insanely jealous, and controlling woman. Synonym - Glenn Close's role in "Fatal Attraction". Alternate Synonyms - see Bitch, Stalker, My Ex.,
My former girlfriend called me 3 separate times on my cell - back to back to back - while I was meeting with my boss, after each time I told her specifically I was with my boss. I was nearly fired. She was not right in the head; I don't care how good that booty was, because it was not good enough to deal with that headcase!
by Toddy D. March 17, 2009
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A mentally deficient person, often due to prior or on-going drug use. Often does stupid things. Can also describe a very forgetful person (again, often due to present or previous drug use).
I can't believe he did that, AGAIN, he should have learned from the last disaster! What a headcase!
by jaywalk August 20, 2006
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