It's also a matter of intent. Intentionally, being a dick is macroaggression. Accidentally being a dick is a microaggression. But this leads to an important secondary matter, that of interpretation. After all, if I'm trying to be a dick, then by my own viewpoint I am macroaggressing. If I'm not trying, then how does anyone know I'm microaggressing? The answer is that someone observes my behavior and decides it is a microaggression.
That leads to the second observation, that microagression is a matter of perception and subjectivity, often by people with chips on their thin-skinned shoulders. It can be an obvious insult, like assuming someone is a drooling idiot because they're a certain ethnicity. But it can also be something pretentious like someone deciding
that the word, "niggardly" is an insult against African Americans even though the word doesn't have racist origins (unlike say, "indian summer"). The attitude is particularly pernicious when the person who perceives the insult is acting as an unauthorized proxy acting on the behalf of an apathetic or completely absent group.
All I can say is that I didn't care before microaggression became a thing and the situation hasn't changed now that I've been made aware of this dire threat to humanity. I think it has to do with the fundamental observation that people can choose not to be insulted by non-insults. Thus, anyone who has a serious problem with microaggressions needs to look in a mirror to see who is responsible for fixing that.