From Longman Dictionary of Contemporary Englishwackowack‧o, whacko /ˈwækəʊ $ -oʊ/ noun (plural wackos) [countable] informal a crazy or strange person —wacko adjective That guy’s completely wacko.
Examples from the Corpus
wacko• He was innocent on grounds of being wacko.• Soon, the talk-show producer decides she has not found Mr Right but a certifiable wacko.• Ruby Wax found some real wackos in West Virginia-loons who use poisonous snakes in religious ceremonies.Origin wacko (1900-2000) wacky 