An extremely strong swear word that should only be used in extreme circumstances. This word formed by the words "motherfucking" and "cunt." It is usually used in a negative way, meaning that it would be used if someone was really pissed off or mad at something.
kid: "THIS MOTHERCUNTING TV DOESN'T WORK!"
mom: "What the hell did you just say?!!!"
kid: "uh, nothing mom I was just messing around with the TV" (laughs uncomfortably)
mom: "that's not what I heard, you're grounded."
kid: "aww man."
A word having the dual ability of calling its recipeient not only "incestual," but also questioning their sexual orientation, by suggesting the recipient is unable to "fuck" and must therfore "cunt" instead.