Green’s Dictionary of Slang

(US) mad, eccentric.

1983		R. Price Breaks 423: I paced Jack’s office, speaking in a whack-a-doo singsong.
2003		Rocky Mountain News 3 Oct. 🌐 Initiative 101, the whack-a-doo proposal that would require the city to implement techniques to ‘reduce societywide stress’ (whatever that means), has caught the attention of The Daily Show, Comedy Central’s irreverent ‘news’ program.
2024		D. Swierczynski California Bear 107: ‘I don’t know if it’s the usual midlife-crisis bullshit or some kind of whackadoo menopause thing’.