I agree with your descriptive examples of how microaggressions often play out in the real world. Except I don't think you go far enough with your description.

Microaggressions can be based on attributes in addiction to race. They may include sex/gender, religion, age, class, sexual orientation, disability status, politics, region/residence, et. al. The list goes on.

I also view microaggressions as being something that can be inflicted by the so-called minority against the so-called majority, as well as vice versa. I realize that's going to be an unpopular position amongst much of the leftist intelligentsia who may be reading this, but I'll die on that hill.