I agree no one sets hard boundaries or has hard discussions on what cheating is to them. That leads to the problems we see. People stick to the usual "social ideas" of cheating that we are familiar with and don't disscus them.

There in lies the irony. You state "not everyone goes out searching for opportunities to cheat" that's true, that statement is in conflict with "subtle acts" you tag as "micro cheating"

These "subtle acts" (it again comes back to what we each see as cheating) you suggested, for them to be full blown cheating people would have to do them with the intent to build upto an affair. It's either people do them or they don't that's why I say there is no micro-cheating.

A caveat is that people do these subtle acts, they're themselves oblivious to how another person chooses to interpret them.