attested from 1883, from the pulling motion required to work the taps.
1935, "tedious and ineffectual person," Amer.Eng. carnival slang, perhaps from jerkwater town (1878), where a steam locomotive crew had to take on boiler water from a trough or a creek because there was no water tank. This led 1890s to an adj. use of jerk as "inferior, insignificant." Probably also infl.
by verb jerk off, slang for "perform male masturbation" (first recorded 1916). Jerk off (n.) as an emphatic form of jerk (n.) first attested 1968.