Green’s Dictionary of Slang

(US gay) effeminately, in an affected, exaggerated manner.

1960		G. Westwood Minority 87: ‘Ninety-nine out of a hundred think we’re all like those bitches that go around talking camp as hell and swinging their hips [Simes:DLSS].
1972		B. Rodgers Queens’ Vernacular.
2003		Baker & Stanley Hello Sailor 138: Of course, this was a denial of the actual enduring power relations, but if enough people on a ship acted camp, then the critical mass could create a feeling of personal power.