Not sure about "tjockskalle" though an "oik" is usually considered to be "thick"; and who would say "plebej" about an "oik"? It's a word full of class prejudice, condescension and hostility - the (lower) middle classes talking about the socially inferior - and thus, by implication, vulgar and coarse. "Buse" comes closer I think, but it's not perfect - perhaps because Swedish wouldn't have the implied class prejudice? Any ideas, anyone?