jerk (n.) Look up jerk at Dictionary.com
    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.
jerk (v.) Look up jerk at Dictionary.com
    1550, "to lash, strike as with a whip," of uncertain origin, perhaps echoic. Noun sense of "sudden sharp pull or twist" first recorded 1575. Meaning "involuntary spasmodic movement of limbs or features" first recorded 1805. As the name of a popular dance, it is attested from 1966. Sense in soda jerk attested from 1883, from the pulling motion required to work the taps.