Other forms: wackos
A wacko is somebody thought to be mad or very eccentric. Some wacko on the phone, a wacko theory, call him a wacko.
It is harsher than wacky, which is affectionate, and it belongs to the family of insults that treat mental illness as a punchline. It is American and informal, and it works as an adjective as well as a noun.
1nounwackoSomebody thought to be mad or very eccentric.
“Some wacko keeps phoning the radio station claiming he's from Mars.”
wacko is an insult.
Also accepted in games: lunatic
WACKo → WHACKed on the head
Somebody who has been whacked on the head once too often, and everyone else in the room can tell.
hooks ontowhack
From wacky + -o.
Etymology from Wiktionary, CC BY-SA