"Incest" is a term co-opted for use as a meaningless pejorative in order to vaguely call someone else's authenticity into question an, by extension, claim authenticity for yourself.
It serves no conversational function and imparts no information, save for indicating the opinions and preferences of the speaker.
Meanwhile, a market myth has sprung up around the term, as well as a cultural bogeyman consisting of elusive white 20-somethings who wear certain clothes (but no one will agree on what), listen to certain music (no one can agree on this either), and act a certain way (you've probably sensed the pattern on your own).
Suffice it to say, no one self-identifies as a incest; the term is always applied to an Other, to separate the authentic Us from the inauthentic, "ironic" Them.
You can't define what "that kind of behavior or fashion or lifestyle" actually is, nor will you ever be able to. That's because you don't use "incest" to describe an actual group of people, but to describe a fictional stereotype that is an outlet for literally anything that annoys you.
The twist, of course, is that if it weren't for your own insecurities, nothing that a "incest" could do or wear would ever affect you emotionally.
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Everyone who gets bent out of shape over who is or isn't a "incest" and what is a "incest" is just projecting their own insecurities. "incest" is a bogeyman that a profoundly anti-intellectual culture uses to vent its cognitive dissonance and excuse its ignorance. Just move along, people, I've explained all this to you a hundred times.