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1. Entirely irrational: Completely unreasonable or lacking any sense of the consequences of actions taken.

2. Affected with dementia: Affected by the loss of intellectual functions that is associated with dementia. This usually only happens to elderly (old) people.
My friend's granpa is demented, he can't remember a thing.
by Jafje March 31, 2007
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2
to be out of one's head on ecstasy in Cork city, Ireland
"i'm fuckin demented, boy!" followed by horrible gnashing of teeth noises
by ros2222 May 31, 2007
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3
Result of sever head trauma, hence, retarded.
-That damn son-a-bitch gowt hit wit dis here club 'n' now he aint say nuthin no more.
-That demented moron looks at walls more than tits
by Urban Dictionary February 27, 2005
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4
adjective
1. Something fairly absurd which triggers illogical or unreasonable laughter.

2. The new random
After I kicked him, he turned around and proceeded to gape at me with a demented stare.
by Ruby "Cuff" Slasher May 19, 2007
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5
Third shift at the Wal-Mart Supercenter in Goshen. See Wal-Mart Mafia
I just went to Wal-mArt and damn those bitches are demented as a motherfucker
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6
The word means mentally deranged, but so far nobody has mentioned how "demented" can be stretched, ironically, to include clownish, wacky etc. Just the thing for the Urban Dictionary!
"That Debussy Sarabande analysis video is totally demented."
"Nonsense rhyme is so demented."
"The Beatles song "I Am The Walrus" is totally demented."
by anassdickcomesoutfrombehind February 23, 2017
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7
A really freaky-lookin' person. Usually the person looks retarded and in space.
Your brother looks so demented.
by freakinweirdo November 20, 2004
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