headcase
Mentally erratic individual
A headcase is someone considered mentally unstable, eccentric, or difficult to deal with—suggesting their head isn't quite right.
The term is informal and mildly dismissive rather than clinical: My neighbor is a total headcase.
In British usage especially, it can imply someone unpredictably volatile or prone to erratic behavior.
Slang for unstable person
- crazyMentally unhinged
- lunaticDeranged or irrational person
- maniacViolently deranged person
- psychoSlang for unstable person
whacko · troublemaker · loose cannon · unhinged · deranged · disturbed · difficult · impossible
Eccentric individual
- weirdoPeculiar person, dismissively
- characterNature, symbol, or role
- originalFirst or inventive
- kookEccentric or strange person
freak · misfit · individualist · nonconformist · maverick · free spirit · oddity · enigma
Disorder affecting cognition or mood
- breakdownFailure or decomposition
- therapyCurative mental treatment
- psychosisSevere reality detachment
- schizophreniaPsychotic disorder with delusions
bipolar · institutionalized · committed · psychiatric ward · treatment · medication · diagnosis · disturbed
Liable to sudden change
- erraticLacking regularity or consistency
- unpredictableCannot be anticipated
- unhingedMentally or emotionally unstable
- temperamentalEasily upset, unpredictable
mercurial · moody · irrational · emotional · explosive · impulsive · manic · hysterical
nutjob
Slang for unstable person
psycho · whacko · troublemaker · loose cannon · unhinged · deranged · disturbed · difficult · impossible · handful
oddball
Eccentric individual
kook · freak · misfit · individualist · nonconformist · maverick · free spirit · oddity · enigma · wild card
mental illness
Disorder affecting cognition or mood
schizophrenia · bipolar · institutionalized · committed · psychiatric ward · treatment · medication · diagnosis · disturbed · unwell
volatile
Liable to sudden change
- erraticLacking regularity or consistency
- unpredictableCannot be anticipated
- unhingedMentally or emotionally unstable
temperamental · mercurial · moody · irrational · emotional · explosive · impulsive · manic · hysterical · unbalanced
headcasewell-adjusted
Psychologically healthy and adaptive
sane · stable · sound mind · level-headed · balanced
headcasestraight arrow
Honest, principled person
rock · low-maintenance · easy-going · dependable · reliable