"Jagoff" (sometimes "jag-off") seems to have
originated in Pittsburgh but is also
recognized in the Midwest as slang for an inept, feckless, contemptible, or generally
worthless person, a loser, a "schlemiel."
The term is almost certainly derived from the verb "jack off" (through noun "jack-off") as in "masturbate," but somewhat like the British use of "wanker," it is usually not a direct comment on self-pleasuring, but more of a general term of contempt or deliberate abuse. Like "wanker," "jagoff" is somewhat vulgar and not to be used lightly, and avoided in cultivated speech, but is recognized by all in the regions in which it has currency.
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The book KILLER CLOWN relates that
John Wayne Gacy became especially flustered or angry when called a "jagoff." So the police
deliberately used that term to throw him off-balance during
interrogation.
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