Green’s Dictionary of Slang

bananas adj.

[? one’s mind or sexuality is ‘bent out of shape’]

1. homosexual.

[US]Ersine Und. and Prison Sl. 15: bananas, adj. Homosexual, queer.
[US]A.J. Pollock Und. Speaks n.p.: He’s bananas, he’s sexually perverted; a degenerate.
[US]Guild Dict. Homosexual Terms 3: bananas, to be (v.): To be homosexual. (Criminal slang.).

2. of a person, crazy, eccentric.

[US]S.F. News 30 Mar. 11: They say you’re bananas!!
[US]Current Sl. II:4 3: Bananas, adj. Fake, phony.
[US]S. King It (1987) 332: You better call your house [...] So your f-folks don’t go b-b-bananas.
[US]S. Morgan Homeboy 209: You’re fuckin bananas.
[UK]M. Coles Bible in Cockney 101: Jesus goes bananas in the Temple.

3. of an object, crazy, unbelievable.

Online Sl. Dict. [Internet] bananas adj 1. unbelievable; RIDICULOUS, CRAZY. (‘That Chris Tucker movie was bananas.’).
[US]‘Dutch’ ? (Pronounced Que) [ebook] The party was bananas. It was filled with young black gangsterzs who [...] were just beginning to taste the good life.

In phrases

drive bananas (v.)

(orig. US) to drive mad, to infuriate.

[US]L. Rosten Dear ‘Herm’ 172: Being so helpful to the Klitchers about many various questions, I have one that is driving me bananas!
[US]J. Sayles Union Dues (1978) 149: With the kids it’s guns and revolutions, not shacking up and driving your old man bananas.
[UK]F. Norman Too Many Crooks Spoil the Caper 159: This dump is driving me bananas.
[UK]Guardian Rev. 23 July 6: That’s when you long for people who otherwise drive you bananas.
flip one’s banana (v.) (also flip one’s raspberry) [SE flip; note flip v.4 (2)]

(US) to go suddenly insane, to lose control of one’s emotions.

[US]A. Pearl Dict. of Popular Sl. 51: – Flip one’s raspberry to lose one’s temper.
[US]H. Montes ‘Odious de Cologne’ [Internet] Mojo Jojo – ‘Aaahhh, refreshing, like a soothing after shave. Not that I ever needed to shave.’ Blossom – ‘Have you flipped your banana Mojo?’.
go bananas (v.) (orig. US)

1. to lose emotional control [image of an over-ripe banana that ‘goes soft’].

Paradise of the Pacific 76 90: Here are five other possibilities [...] designed to keep you from going bananas, except, of course, culinarily.
[US]S.F. News 2 Sept. 30: I n-never knew goin’ bananas was contagious!!
[US]E. Grogan Ringolevio 227: He went bananas [...] because of some severe strain.
[US]T. Wolfe Bonfire of the Vanities 215: They got three homicide witnesses over here chained to the fucking desk legs in the Detective Bureau, and they’re going bananas.
[UK]K. Lette Llama Parlour 222: When he can’t find it he, like, goes bananas.
[UK]B. Hare Urban Grimshaw 63: Greta went bananas.
[UK]Observer (London) New Rev. 19 Feb. 7/2: He only did ‘Shut Up,’ but the crowd went bananas.

2. to delight in something absolutely; usu. as go bananas over.

[US]G. Underwood ‘Razorback Sl.’ in AS L:1/2 56: bananas, go v phr [...] 2: Enthusiastically approve of or find pleasure in something.
[UK]Guardian Guide 31 July–6 Aug. 40: Go bananas at Ape’s birthday party.