Meiko, please: "Even blacks call each other nigger when they feel like it." is a statement which, at best, deserves some further qualification. As it stands, it is provocative to say the least. I'm sure you don't mean this, but please let us know otherwise.
Yes, "Cracker" is a pejorative term, but its etymology is so obscure and dilute (
http://en.wikipedia.org/wiki/Cracker_%28pejorative%29) that I defy any caucasian to deny the vastly more pernicious effects that the epithet "nigger" would engender.
This is delicate ground. Tip-toeing is advised.