Fucken fuck can be used in many ways. My favorite way to use it is when you can't find something but you know its there but you're so pissed off that you just yell Fucken fuck. Or if you're losing at a game, yell fucken fuck.
"Dude, where'd those tabs go for my guitar? Fucken fuck!"
This is a more offensive way of calling someone of fucker. The person saying it is very angry and the person being called it has done or said something very stupid.