An actual microaggression is something like when you're a security guard and you follow someone around in the store just because they're black.  What most people call a microaggression is more along the lines of someone looking surprised after seeing someone who is black even if they come from a place where there aren't many black people. Edit: Basically it's something that could be called "racist" (or sexist or whatever) but it's not in your face, like calling a black person a "monkey"