Green’s Dictionary of Slang

bamboo adj.

[a very common plant in the area]

1. (US) Chinese.

[US]Ade ‘Hickey Boy and the Grip’ in In Babel 110: Me settin around on my shoulder-blades lookin like one o’ these bamboo boys full o’ hop.

2. used of a Westerner who has ‘gone native’ while stationed in the Far East; thus of the accented Eng. some use (see cite 1934).

Hospital Corps Qly 20-23 31: [...] eventually earning for themselves the contempt of their more self-respecting shipmates and being rewarded with that most degrading of all titles known in the islands as ‘Bamboo American’.
E. Hahn China to Me 117: [His accent has] a little bit something else hard to describe, although a lot of people out East get it. We call it ‘bamboo American.’ I am tainted with it myself, I suppose.
[US]Life 28 Oct. 99: Squacks are the native girls of the Pacific sometimes taken to mistress by sailors who assume the title of Shackmaster, and become Bamboo Americans.
W.L. White They Were Expendable 97: There was, for instance, a bamboo American— some man who’d married a Filipino wife and gone native— who managed a big pineapple plantation.
Fraud & Corruption in Management of Milit. Clubs 877: An inquiry into Crum's background showed that he was a so-called ‘bamboo American,’ having been born in Shanghai, China, in 1918, and having lived most of his life in the Far East.
J.H. Bishop Coll. of Stories 77: Bamboo Americans are former American soldiers and businessmen, usually married to Asians, who after World War II or Vietnam loved the oriental lifestyle [...] and never went home.
(con. WW2) P. French Through the Looking Glass 213: Durdin was still working for the New York Times and was by now firmly a bamboo American but he never became overly pro-communist.

3. eccentric, mad [f. sense 2].

[US](con. early 1950s) J. Peacock Valhalla 322: Was he going bamboo? No, he wasn‘t going bamboo. He knew what he had to do.