Definition of "bananas"

I am astonished, really astonished, that you didn't put away some dough. You must be bananas.

1976 September, Saul Bellow, Humboldt’s Gift, New York, N.Y.: Avon Books, page 377

The ensuing snarknado also seemed to goose the TV ratings. Hundreds of thousands of viewers switched on the movie after it began, suggesting that they’d gotten wind through Twitter of the bananas spectacle that was unfolding.

2023 July 10, James Poniewozik, “The Twitter Watch Party Is Over”, in The New York Times‎

“September was, in my professional opinion as a climate scientist, absolutely gobsmackingly bananas,” said Zeke Hausfather, at the Berkeley Earth climate data project.

2023 October 5, Damian Carrington, “‘Gobsmackingly bananas’: scientists stunned by planet’s record September heat”, in The Guardian‎, UK