na-adjective
Slang abbreviation of 頭がおかしい (atama ga okashii). Used informally to describe someone or something as crazy or out of their mind.
See also: 頭がおかしい
あの先生、宿題を毎日100問も出すとかあたおかだよ。
That teacher is insane, giving 100 homework problems every day.
こんな時間にカラオケ行こうって
Wanting to go to karaoke at this hour—isn't that crazy?