Can i be fired if someone heard me say the n- word ?

Customer was really nasty and rude to me . I didnt say anything to the customer. But when the customer left ,i said , i hate when people act like" the n word" . An other employee heard me, and i said sorry for my comment , the emplyee said it was cool and started laughing then repiled,the customer was really rude anyway. The next day the employee told my boss and i was let ask to resign because that employee was offened. I feel like i shouldnt be fired since the comment was not direct to any one. It was my oppinion about some one else out side the work place.