Having someone call you a McFlago means you are insanely awesome and proud of it. You show off an aura of sophistication, Glory and Divine Awesomeness amongst others. It is common to also be found irresistible by men and women alike.
Could also imply you have a big penis and you are proud of it.
Alex: Hey Stephen, Your such a McFlago!
Stephen: Thanks man!
Alex: No really.. Your eyes.. are beautiful like tall.. blue mountains..