Extremely demented, or entirely messed up looking as if it really was demented. Stupid or dumb looking.

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.

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!

Someone who has a negative influence;

Causes the world around them to turn to appear deranged.

Unintentionally creates conflict and bad moods to anyone around them.

Attracts negative spiritual energies and entities.

a total and complete loss of logic and reason, dementation is the way forward, dementation

to be out of one's head on ecstasy in Cork city, Ireland

Result of sever head trauma, hence, retarded.