I didn't find the rank ups so amusing later on, probably because I've never played a CoD game online.
But I've always wondered if they create an infinite number of fake ranks.
In MW2 it goes like this: Private, Private I, Private II, then Private First Class, Private First Class I, Private First Class II, etc.
It looks like Black Ops walked a dangerous line and changed it to Private I, Private II, and Private III, but I don't think that one backfired on them too much.
EDIT: The level cap in MW2 was 70 though, so that's still something like 34 unique names if you discount the numbered variations.