Leeroy officially became a cuck when he started blog posting about male privilege; his hopes and dreams of getting laid from this never came to fruition.
"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).
A man who allows their wife or girlfriends to have sex with other men. He would also apologies if their wife is cheating on him. A cuck is very different from a simp. A simp is a man with is desperate for pussy and will bend down or bow to a women to get a chance while a cuck is a man who has the pussy but will happily let other men tap or wank to the pussy.
A person who is confused for a simp but is actually a cuck is iDubbbz as he has a girlfriend but will happily allowed her to show off her body.