A word to use if you're sick of taking the time to say motherfucker. Plus it just has a better ring to it, and is superior to the crappy gangsta version mofu.
Scenrio with motherfucker:
Some asshole cuts you off on the highway. You lean out the window and yell "MOTHERFUCKER!" at him and by the time you finished yelling motherfucker he has thrown a tire iron at our head, knocking you out, and you crash and die.
Scenrio with malfuck:
Same thing happens on the highway. You lean out and yell "MALFUCK!" and have time to squeze back into the window while a tire iron goes zooming past your head. You run the son-of-a-bitch off the road.