The vehicle of "that Mustang guy" who is obviously better than you because he has a Mustang. Every story or conversation eventually reverts to his Mustang which more often than not has "500 horsepower." Muff-tangs are usually associated with tools
, Affliction/Ed Hardy clothing, and slightly sideways flat-brim hats on white guys.
"Did you hear that fag with the Ed Hardy shirt talkin about his Muff-tang again?"