Green’s Dictionary of Slang

(US) a masochist, thus maso-sissy, a homosexual masochist.

1963		J. Blake letter 17 Feb. in Joint (1972) 202: Doug is capable of a vicious chilling cruelty that can be too much for a maso like me.
1967		J. Herbert Fortune & Men’s Eyes 18: I’m no maso-sissy, sad-ass, I always kick for the balls when attacked [Simes:DLSS].
c.1972		‘L. Harrington’ Satan’s Stud 48: ‘The old maso must have really got his kicks’ [Simes:DLSS].