To many US blacks, "cracker" also means white racist, and not the passive sort that mumbles nasty things privately-- rather, one who rides around in a pickup truck looking for little black girls to rape or big black men to hurt or kill, which still happens. One connotation is the cracking of the overseer's whip. Thus, all sorts of harms are assumed to be expected from a "cracker," including economic, social, political, and physical. The term in use in that context is dismissive and defiant.... if the white person is thinking (or saying) "you nigger,", the black person may be thinking (or saying) with equal fear and enmity, "you cracker!"

It isn't only US/UK that are divided by a common language.... when a white person calls a white person a "cracker," it's classism. But when a black person calls a white person a "cracker," it's got all the fear and force of racism loaded into it.

~Susan