Impolite behaviour is impolite behaviour, whoever is on the receiving end.

The racist person can be rude. The rude person is not necessarily racist. But there are racists who are always polite, even to PoC, and that does not alter their racism a fraction.

Appropriating every slight, every left-handed comment, every piece of everyday bad manners, and making it racist because it happened to the Black person is less than helpful.