An equal-opportunity racial slur to reference a white person. Similar to calling a person of the continent Asia a "rice nigger." If "nigger" can be associated with any person, rather than just a person of African dissent, plus by placing the most stereotypical food consumed by that person's culture, as an adjunct to "nigger," then it can be assumed that bread, a food predominantly responsible for the survival and prosperity of Europeans, relates to Caucasians. This term can be taken as a neutral slang term or pejoratively, depending on the context and intention of the speaker. (i.e. Among whites, this would not be offensive to the receiver. If a black person used it against a white person, however, the term would likely be perceived as spiteful. Moreover, it would be facetious, comparative to a situation in which a white friend would jokingly call a black friend "niggah.")
"I can't stand bread niggers."
"You're a good-for-nothing bread nigger: raper of peoples, harbinger of wars, denier of truths, and the most fearful of all people."