Why is "discrimination" and/or "prejudice" only used to when it is the majority acting toward the minority?

When a person attacks a heteroual person for being straight it is usually viewed as "honorable" because she is "sticking up for her beliefs" (Rosie O'Donnell), or when a minority stereotypes and makes fun of a white person it is viewed as "comic relief" (Dave Chappelle). Why is this type of stereotyping and discrimination acceptable, when a straight, white person cannot "make jokes" about another race or ually oriented person or "stand up for their rights and beliefs" without being considered a bigot, racist or phobic? I understand that most people have a natural tendency to prefer others like themselves. I’m not saying that we should all badmouth each other (I actually believe quite the opposite), but the same rules should apply to all. "Equality" does mean for people to be treated equally, right? "Discrimination" is discrimination and "prejudice" is prejudice, regardless of race, religion, ethnicity, gender or lifestyle.