Stereotypes cause offence to people when the people in the group being stereotyped feel insecure in their own identity. This can be for valid reasons such as, given their socio political history, black South Africans taking understandable offence to racially derogatory language used by white people. Or for non-valid reasons such as people being jumped up privileged idiots with a skewed sense of their place in the world. ?But this means that there are different rules for different people? You say. Yes, yes it does. But they are not rules, just general guidelines on how not to be a dick.