by 1940s, Amer.Eng., from cock
(n.1) in phallic sense + sucker
. Used curiously for aggressively obnoxious men; the ancients would have understood the difference between passive and active roles; Catullus, writing of his boss, employs the useful L. insult irrumator
, which means "someone who forces others to give him oral sex," hence "one who treats people with contempt."