A mustache variant. Specifically, a mad dog (or Hulk Hogan if you prefer) that only combat Vietnam vets can grow after they've reached the age of 55. Only after you have looked eye ball to eye ball with the man in the black pajamas (a worthy fucking adversary) will you be able to grow this mustache.
Most, if not all, of the gentleman sporting this stache will be wearing a Vietnam Veteran hat and a pair of gold aviator sunglasses They may, or may not, also have a kick ass nickname, like "Dead Eye" or "Bunny".
Is your uncle Jack a porn director or a Nam vet?
You can't tell from his supreme nam-stache? I thought it was obvious!