Here are my standards:
Active Duty Marine - A Marine currently serving on active duty
Marine Reservist - A Marine that is currently in reserve status
Marine Corps Veteran - A Marine that has successfully completed enlistment and/or commission in the USMC
Former Marine - An individual who, for what ever reason was separated on Other Than Honorable, or worse, circumstances from the Corps. In my book, this title also includes individuals who no longer uphold the values of the USMC in their personal and political lives; although some people would argue that point.
Wouldn’t there also be a “Retired Marine” (one who made it a career)?
I thought Former Marine is one no longer on active duty and/or no longer in the Reserves and Ex-Marine is someone who dishonored himself by dishonoring the Marines/the country, i.e. Murtha.
Former Marine thus fits for Former Congresscritter John Murtha (censored) - now a crispy critter.