In both cases, it seems to work more as extenuating circumstances than as a blanket permission to say inappropriate things to another human being based on his looks. Or in other words, it's not OK to discriminate against somebody else solely for the reason that you are part of a group discriminated against. It just makes you part of the problem.

I think having a definition of racism to be "discriminate against somebody else due to skin colour", as well as a notion of "institutional racism", which is the same thing but on a systemic level, would make more sense than the more academic definition of racism.