The idea of using anyone’s name, white or black, as an insult: it’s not a good one.
The one Karen I know is a really decent human — a lifelong union organizer who has struggled to raise two kids after her husband left. The only Becky I ever met was a young girl who was a librarian.
(I won’t also add examples of people using typically Black, male names as racist slurs, because why give them a platform? But we both know these exist.)
Instead of using nicknames that have collateral damage on humans you might actually like, why not just actually call people what they are? Words like “bootlicker”, “racist” or “snob” are not just more accurate, they’re more likely to actually wound the target.