✔ 最佳答案
The white boss "whip cracker" to the slaves back in the day.
Blacks shortened it up to "cracker" or as some of the hood rats say "cracka".
It is ment to be insulting to white people.
You could call another race a cracker if you want to, but most always here in the U.S. it is only used by blacks toward whites.
BTW your English class is correct, a cracker is a thin biscute waffer to be eaten as food. It means that in the U.S. as well.