loony

nouns

someone deranged and possibly dangerous
crazy, looney, loony, nutcase, weirdo

adjectives

informal or slang terms for mentally irregular
"it used to drive my husband balmy"
around the bend, balmy, barmy, bats, batty, bonkers, buggy, cracked, crackers, daft, dotty, fruity, haywire, kookie, kooky, loco, loony, loopy, nuts, nutty, round the bend, wacky, whacky
is derived from
loon