I know many Manchester United fans who are from Manchester, that joke/argument is pretty much dead. Also, I don't know whether its intentional or not but do not refer to Manchester United as 'Man U' or 'ManU'. Here;s why:
ManU is not a term Manchester United fans refer to themselves as. This term is only used by rival supporters as an insult to our beloved football club. The “u” is meant to be “you” by the rival fans. An example of its usage is a chant by WBA fans: “Duncan Edwards is manure, rotting in his grave, man you are manure- rotting in your grave”. So the origin of “ManU” is a song to insult the dead Duncan Edwards.
Both Liverpool & Leeds fans copied this with their own man you/u versions to insult all those who died at munich. “ManU ManU went on a plane ManU ManU never came back again” and.. “ManU Never Intended Coming Home” (combine the capital letters and you get the word “munich”).
Manchester United 2008-09 Season - Trophies & Records