A pejorative term for a White person in the United States who takes it upon himself to assume authority over others they deem inferior without any official justification often in an indignant or self important manner.
When used as an insult, it is a metaphor in the sense that when herding animals, the owner hires working class men to crack a whip to tend his herd. The herders or cowboys have no real authority other than to crack the whip and do what their boss says - the man with the real power. When used as a slur, 'craking the whip' means to run ones mouth, complain, rant, bitch and moan, blog, etc because as a schlub, that is all he can do; essentially a wimp.
Don't listen to what crackers have to say, all they have is their words.
The only thing worse than a cracker is a cracker with a badge, they think the own the place.