expression, noun-modifying (irregular)
insane; crazy; out of one's mind
Colloquial, often derogatory expression describing someone as mentally unstable or acting irrationally. Used prenominally to modify a noun.
See also: いかれる
That crazy guy is shouting loudly again.
Don't say such insane things.
Katakana spelling of いかれる adds emphasis or a slangy feel.
Phrase composed of 頭 (head) + の (possessive particle) + いかれた (past attributive of いかれる 'to go crazy'). The verb いかれる is a colloquial passive/resultative form of 行く (to go), implying 'gone' in the sense of mental departure.