Someone who fucking fucks.... Fucking is a verb so it just tells you that the "fucker" is doing just that. Fucking. He is often found being a noob. Or when you yell at someone and you have nothing better to say than "YOU FUCKING FUCKER!!!"
Dillon: I cought a fish that was this big.
Jesse: I counght a fish that was thiiiiiis big!
Nolan: My ASS!! you fucking fuckeR!!! I got one this big!!!!!!!!
Dillon: Nolan, but your penis away and show me your fish...