-rep "Cuck" a weak, feckless, spineless, and decidedly pathetic specimen of manliness. It is a dirative of the term "Cuckold", which in turn comes from the now extinct Cuckoo Bird (known for laying its eggs in another bird's nest; kind of like how a cuckolded man lets another man screw his woman).

Word Origin: In mid 2016 the term came to prominence when supporters of Donald Trump came to refer to Republican presidential contender Jeb Bush as a "Cuckservative" (cuck+conservative), implying that he was a weak, testicle-lacking, creampuff of man, and a poor representative of what Trump-supporters considered proper GOP presidential timber. Jeb responded by effectively proving them right. The term Cuck has since taken a life if its own as an insult towards anyone who comes across as femmy, weak, or lacking in enough testosterone to get their balls to drop.
"Did you see that ♥♥♥♥♥♥♥♥ Jeb Bush outright *beg* that crowd for an applause? What a cuck!"

+REP is me