German speakers, please help

Recently I've run into the German term "warmer Bruder" (warm brother). I know it's slang for a gay man, but I'm wondering about connotations. Is it derogatory? And, to the best of your knowledge, would it have been derogatory in the 1940s? (I.e. is it a term like "Negro" in English that has moved from being standard/polite to being objectionable?) Google has not really helped me with this, although the term does turn up in a list of German expressions that foreign speakers should avoid using.