My favorite non-names of background characters:
1) In The Blues Brothers Movie, there was character --a grizzled old man-- who lived in the same flop house as Elwood Blues. As Elwood was walking into the front door of the flop house, the grizzled old man was sitting at the far end of the lobby and spotted Elwood entering. He called out to Elwood: "Did you remember to get my Cheese Whiz?" All in one unbroken motion we saw Elwood wordlessly reach into his pocket, pull out a can of Cheese Whiz, and toss it across the lobby into the ready hands of the old man. The old man caught the can and instantly pulled out some crackers and started spraying ribbons of Cheese Whiz onto them.
That was the ONLY instance of that character in the entire film. We never saw that old man again, we never heard anyoe mention his name -- nothin'!!
When the credits rolled at the end, we saw a credit for a character whose name was listed as "The Cheese Whiz." (I laughed out loud when I read that credit.)
2) In George Romero's Land of the Dead, we saw a teenaged zombie girl wearing a LaCrosse uniform (or maybe it was a field hocky uniform I don't recall which). The number on the front of her uniform was a 9.
When the credits rolled at the film's end, we saw a credit for a character named "Number 9."
I always try to make up semi-legitimate names for my "non-characters" from two prespectves. First, from the perspective of the actor trying to fit the acting credit somewhere on his/her resume, becasue if the actor has nothing but the same-old-same-old non-character names like "Cop #2" and "Third Henchman" all over his resume, that REALLY sucks, but "Numebr 9" and "The Cheese Whiz" are eye-catching. Second, from the perspective of the audience reading the credits at the end, because the audience WILL remember the whole Cheese Whiz moment, but will probably be confused and draw a total blank if they read a vague and unimaginative credit for "Old Man in Flop House Lobby."