No it isn’t, it’s a reference to a Perry Bible Fellowship comic https://pbfcomics.com/comics/skub/
(This one is sfw, not all of the comics are)
Even urban dictionary doesn’t contain a definition for skub as a slur.
(This one is sfw, not all of the comics are)
Even urban dictionary doesn’t contain a definition for skub as a slur.
What about this then: https://en.m.wiktionary.org/wiki/skub