Green’s Dictionary of Slang

(US) a homosexual thug.

1940		G. Legman No Laughing Matter (1975) 131: ‘I was in Atlanta, Georgia, [...] and this big baytzimmer [...] grabbed me by the neck and said to me, “You’re going to suck my prick..”’ [Simes:DLSS].
1975		G. Legman Rationale Dirty Joke n.p.: ‘Baytzimmer’ actually means a person with large testicles and—therefore—a small brain, in Jewish folklore and folk-speech.