Micro-aggressions are all those little things people do to other you or put you in your place. They are usually small, easily unnoticed by those who aren't the targets. And, as they are usually so small, if you do call them out you are perceived as over-reacting or oversensitive.
Examples include things like, upon meeting a professional woman for the first time, asking how she balances work and family. It's just a 'polite question', but it's not one most would ask a professional man and thus it is meant to call out that she is different and suggest that her priorities should be questioned. But if she calls it out as such, well, then she is being rude because you were just asking a polite question, right?
Other examples include the 'so where are you really from?' questions of ethnic minorities, addressing a woman by her first name but a man by Mr. _______, insisting on giving unnecessary help or advice, ignoring all of a person's actual accomplishments to congratulate or identify them instead on something having to with their gender, disability, or ethnic background, or declining to let a person of a particular gender/ethnicity assist you when you would have accepted the help from someone else.
My black male friends are full of stories of people on the bus protectively switching their briefcase/purse to the opposite side. Whenever I go shopping with my husband, when I pay the card/change/receipt is often handed to him. More blatantly, questions I ask are answered to him, or answered very basically while questions he asks are answered thoroughly. My Asian female friends can't get through an interaction with a stranger without being asked what part of Asia they are from, even the ones who are 5th generation Americans. As a professional woman, I deal with a lot of 'Here is Doctor X who studied the primordial sloth, Professor Y who built a TARDIS in a cave with a box of scraps, General Z who programmed the first positronic spaceship, and Garden who is married and mother to one kid'.
By far, the most common micro-aggression for myself and all my female friends is being told to 'smile' as we are trying to go through our daily lives.
The point of this post is that, well, these aren't okay. It's discrimination. It's low-level bullying. And a lot of folks aren't even aware that they do it, let alone that their victims might find if offensive.
When victims do call out these behaviors, please don't respond by suggesting they are overreacting, or should just get over it. There is a lot of straw on the camel's back already, you don't need to pile on more once it's already broken. And try to examine your own behavior at times to make sure you aren't inadvertently engaging in many of the same behaviors.