Some poor soul whose last name just happens to involve a spelling very similar to 'fail', and everyone else picks up on the last syllable, and thus the person becomes a macfailure.
Person One: So, what's your last name?
Person Two: MacPhail.
Person One: As in, like, you FAIL everything? *laughs*
Person Two: *Bored* Yes, exactly like that.
Person One: You're a MACFAILURE!
Person Two: Wow, thats the first time i've heard THAT one!