Green’s Dictionary of Slang

j.o. n.

[abbr. jerk-off n./jack off v.1 (1)]

an act of masturbation.

[US]B. Rodgers Queens’ Vernacular 116: mutual masturbation by two men. [...] hand job masturbation performed by one man upon another [...] JO.
OutRage (Melbourne) Sept. 17/3: [H]e has just joined a gay nudist club in which the prospect of group JO is always present [Simes:DLSS].
[US]Chapple & Talbot Burning Desires 303: The exposed nature of J/O parties also made it virtually impossible for overheated celebrants to break the rules and conjoin their bodies.
[SA]K. Cage Gayle 77/1: JO (abbr.) jack off, masturbate • JO club gathering of men for the purpose of masturbating together (cf. circle jerk) – these clubs became popular in the late 1980s as an alternative to unsafe sexual practices such as fellatio and intercourse.

In compounds

J.O.-artst (n.)

1. (gay) a dedicated or skilled masturbator of oneself or another.

[US]P. Roth Portnoy’s Complaint 204: Oh, you jerk-off artist ! You case of arrested development !
[US]J, Michael Do It Up Brown 113: The hippie was a good jerk - off artist ; he knew how to use his hands . I wondered whether he sucked.
[US]Christopher St 7 31: I’m a jerk-off artist and a very good one , I think . After all , it's prob- ably the longest standing sexual activity we have experienced.
[UK]J. Collins Lady Boss 367: He was flitting around behind the trees like a secret jerk-off artist.
[Aus]Pump It Up Spring 52: [personal advert] Hardcore auto-fellator and J/O artist seeks friendships/adventures [Simes:DLSS].
[US]R. Liebmann-Smith James Boys x: Do we [...] even care if William James [...] was a major jerk-off artist.

2. a general term of abuse, a time-waster.

[Aus]Capital Q. (Sydney) 26 Feb. 69/1: [personal advert] Beginners or experienced welcome, but no time wasters or JO artists.