Charlie

Of all the racial slurs ever uttered, "Charlie", for a Vietnamese person, is probably the least inherently offensive. IMHO.
The closest equivalent I can think of is "Jerry" for a German person. Oddly, Wikipedia does not describe "Jerry" as offensive.
"Charlie" was specifically used for enemy Vietnamese, and the etymology was simply the use of "Victor Charlie" (military radio code) for "Viet Cong", or North Vietnamese irregular army.
Which makes it interesting in the world of slurs.
Now, make no mistake, calling everyone who is your "enemy" the name Charlie does indeed help to de-humanize them. That is, perhaps, explicitly the point of using slurs. But "Charlie" has the perhaps unintended affect in that it's also a somewhat friendly-sounding name (in English).
The way it's not used is when speaking to an individual North Vietnamese person. For instance, you can imagine someone calling to an American soldier "Hey Joe -- you want to buy some of my wares?" Or to an English soldier "Hey Tommy -- you want to buy some of my wares?" But "Hey Charlie..."? Nope, doesn't work.

Now, note that it's patronizing to call all English "Tommy" and all Americans "Joe". And also note that there isn't really a big tradition of Vietnamese soldiers being in other (well, Western) countries. But who knows? (What did Cambodians call the Vietnamese soldiers?)
But what is just patronizing, what is downright insulting, and what is completely neutral always changes. Just look at the attitudes of different generations toward different words for African-Americans. From the n-word, to negro, to colored, to black, to Afro-American, and now there are even some that insist that the n-word is completely acceptable again.*
It's difficult for a lot of people to understand (or even remember) that "Asian" is acceptable while "Oriental" is not. What makes that even harder is that a bunch of older Chinese still call themselves "oriental". Yeah. Language is wacky like that.
So, you're asking yourself, "where are you going with all this?"
Nowhere, actually. My goal was to come up with the name we'd call the aliens in the future. "Dave", "Zoroaster", "Andy?" I got nuthin' 'cause none of it has any cultural weight. It sort of feels right to call your enemy "Charlie" (which, as far as I know, is simply not used by American racists to refer to any Asians) when thinking of it outside of the "slur" and just from a dialog point of view (I've been watching Apocalypse Now, do forgive me.)
Maybe we should just call all humans NooBs...

*Not to this white guy, but to others perhaps.