If people do not know they are racist they would be more open to listening to explanations of systemic discrimination. Speaking to them rudely doesn’t solve anything or calling them racist when they have not taken the time to understand what systemic racism is. Asking them to think about the difficulties that people of colour have in the present system and trying to solve better access for all people is problem-solving. Outright hateful racists are another story and very disturbing to have to stand up to blatant in your face hatred. The best choice of action in this situation is to say something brief and short and get out of the situation as racists want to incite bad behaviour to justify their bad behaviour. This is a complex difficult subject with alot of work ahead to create a socially just and equitable society.