A Marine is a Marine for life! He is a Marine from the yellow foot prints in Boot Camp, till the day of his death and beyond. Even after death, "once a Marine Always a Marine". It is considered rude and impolite to call a Marine and Ex-Marine. He can be referred as an Inactive or Retired Marine.
Joe: That Tom is still hard core! Didn't he get out, like, two years ago?
Sam: Yeah, He is an out going Ex-Marine!
(Tom apears from no where in a puff of smoke,and slaps the hell out of sam and states loudly ("Semer Fi For Life").