Medi, your definition seems to conflict with the one several other people have used, in which they argue that microaggressions are generally unintentional things brought about by obliviousness.
Someone deliberately being an ass should properly be slapped down, whether the offense is micro or macro.
There's a thing that happens when term of art/jargon enters the public sphere where it can evolve in meaning. This is the nature of language.
I would also argue that quite often people say that they didn't intend something when the fact that they did it/said it suggests otherwise. They may, for instance not intend to be racist/sexist/etnocentric etc. but
they intended something, even if was the satisfaction of vulgar curiousity (my grandmother's turn of phrase).
In some instances, the intent is a social putdown, of the "and your mom dresses you funny" kind of thing gone wrong or taken to excess or engaged in by someone who has absolutely no social acument and is generally horrible to everyone, without even meaning to be aggressive.
In the cases of the two examples I discussed, the intent was to validate the two aggressors' personal senses of superiority by invalidating someone else. People do that all the time. We are not all that different from chickens, and we too have
pecking orders.
When someone does something that they know is not acceptable in terms of basic courtesy and they do it anyway, they are deciding they have priority over the other person. Sometimes there's a reason for that other than aggression. A lot of times, there isn't.
And like so much of language and human behavior, context is all.
Some recent, more academic but still sensible discussions:
https://www.psychologytoday.com/blo...y-life/201011/microaggressions-more-just-race
http://www.apa.org/monitor/2009/02/microaggression.aspx
http://www.nationalreview.com/article/370078/microaggression-alec-torres
Keep in mind my personal bias. I think Sapir-Whorf were on to something, and that language does shape thought.
There's a point where people take this stuff to absurd lengths, but if you look at the middle range of the spectrum, there's a lot we can do better about how we interact with others.