I added one. It's under review. It's very self referential.

>Even urban dictionary doesn’t contain a definition for skub as a slur.

What about this then: https://en.m.wiktionary.org/wiki/skub

That literally defines it as a word from the PBF comic I cited? Nothing on that page defines it as a slur, just as a word used to mock people who argue about inconsequential things.

Seems I misunderstood the notion of "slur" as I'm not a native speaker. So now I've learned a bit ;-)