A child who is conceived through a good fucking as opposed to an act of love. Often used after the word bastard to strengthen it - bastard fucklet - , thereby implying the child was not only conceived out of wedlock, but also from a loveless screwing - a good fucking.
Could just be a simple insult that a joe six-pack might shout at his child:
Lit., "fuckingknucklehead" Usually reserved for someone who stubbornly adheres to false principles or consistently acts irresponsibly; generally, an idiot.
"She hates your guts, you fucklehead! Quit calling her!"