(くるう) Someone who has been insane since childhood. Ted Bundy or whoever. They might seem normal at first.   $$$
きちがい Crazy fucker. Discriminatory term against the mentally ill. One of the worst insults in Japanese.
いってる Someone who is obviously nuts – a street person with Hefty Bag shoes or whoever.   $$$
(はっきょう) Someone who is normally sane but had a breakdown from stress, or a sudden flip-out.