Earlier quoted context omitted.
There's malice and then there's perception. One could certainly look at just about any colloquialism without intended malice and draw "microaggression" from it. Knowing where to draw that line is not - nor has it ever been - universal.
You're literally describing what microaggressions are: Small interactions, any one of which is harmless and without ill intent, which accumulate over the course of the day, week, or lifetime as an atmosphere of pervasive discrimination which is completely invisible to those responsible for creating it. Microaggressions are insidious precisely because they're so innocuous; they let well-intentioned people participate…
> harmless and without ill intent
ag·gres·sion əˈɡreSHən/ noun hostile or violent behavior or attitudes toward another; readiness to attack or confront.
Aggression is, by default, defined by intent, not perception.
> You're a well-meaning person, and you want to avoid causing unnecessary harm with your words. So when you're around people who have really different life experiences than you, how do you make sure you don't cause harm without meaning to?
This was my point about there existing no universal set of social rules. So when someone says "don't say X, it's offensive," I have a tendency to look at that as more a matter of latter-day Tumblr cause celebre than anything real.
As a matter of brutal honesty, when someone tells me that X is offensive to them, I respond by not doing X anymore. I don't accept wide swath rules about such things and apply them universally, unless I observe them with any frequency in the wild. If we all cast that net, communication would be extraordinarily difficult and language impossibly rigid and uninteresting.