Microaggressions are defined as "brief, everyday exchanges that send denigrating messages to certain individuals because of their group membership". The hardest part is that they don't sound aggressive.
Although I'm not part of an oppressed group, I've been microattacked more than once, by the same person.
At some point, he mentioned that one couldn't talk bad about someone "around some people". That "someone" was a politician that got arrested for, basically, stealing from the country to promote a certain other company. The way that person said it, thought, made it seem I felt it was wrong to arrest the politician.
Another time, I was casually saying that I shouldn't have come to work on my motorbike, although three forecast apps said it wouldn't rain. His comment: "I just looked outside".
It may seem innocuous reading those, but if you look closely, all he was trying to do was do let me down. Oh no, I'm part of a group that thinks politicians shouldn't be arrested! Oh no, I'm not smart enough to look outside, while he is1.
And those are really hard to fight, 'cause we aren't prepared to "get" those as real attacks.
The worst part? While you don't fully get it as an attack, it will slowly pile up. At some point, you may even burst into attacking the person back, with all the concentrated attacks in a single moment. And them you will be seen as aggressive, not them.
Better just stay away and avoid contact if possible.
In the end, when I had to leave work to go back home, it wasn't raining.
... which is the pure definition of "Schoddinger's Asshole": Someone that make a comment and, by the other people reaction, call it a joke as a "get out of jail" card.
And I do wish you have a HR department that understand microaggressions.