"Peckerwood" is a good one for whites that isnt that well known. If one of the like 2 at most black ppl that use this site see this: you're fucking welcome.
"Coonass" is great but has limited appeal as it's just for hicks from the bayou, but if you're ever in Nawlins go nuts.
For blacks "bluegum" takes the cake.
But it's honestly hard to choose, theres so many slurs that are ace.