MUH-FUH is used as term for saying mother fucker. It was originally used so that teachers or coaches couldn't understand the fact that you were saying mother fucker.
A complicated idiom used by small, loser-ish people to describe something with great enthusiasm, can be used both positively or negatively. Used in place of words such as motherfucking, or m'f (em effing)
Me: STOP! You're getting on my nerves!
Loser Girl: Ugh! you're so muh'fuh'effing annoying!
Boys who enjoy yaoi (a genre in Japan that contains sexual and/or romantic relations between two men); literally translates to "rotten boy"; corresponding female : fujoshi