Same as "jerk off" (
masturbate); also used as a noun to reference a feckless, no-account person, usu. male.
Up until the 1980s, "jack off" was considered more a Southern (
USA) locution than "jerk off," which was considered more urban and Northeastern/Midwestern states. Considerable swapping around has taken place in the meantime, probably because of increased social mobility and relaxed codes of
censorship.
.
1)...All little Timmy can talk about is sex. If I weren't so polite, I'd have told him to
go get laid, or to jack off in a corner...
2)...'If y'all boys didn't jack off so much, you might amount to something.'... (closet-case coach to members of the
high-school
basketball team in 1971 movie THE LAST PICTURE SHOW).