I saw a male recently who served in the Vietnam War and was active duty from 1966-68.
I made a definite mistake when I asked, "you were a Marine, weren't you?"
He immediately, appropriately, re-informed me that he was "still a Marine; once a Marine, always a Marine."
I acknowledged my error and he seemed to accept it.
It wasn't until I was leaving his home that I also saw a Marine bumper sticker on the car in the driveway that read, "Not as lean, but still as mean."