If hipsterism is a rejection of classical fashion and preppy coolness, posthipsterism is an attempt to escape the dichotomy of geeks and jocks, shaggy hair and clean cut, cheerleader and vegan, guitar playing douchebag and captain of the football team.
Posthipsterism rejects the idea of a cultural truth, that things are inherently fashionable. The posthipster knows that everything is relative, that admitting you like a blockbuster movie can be every bit as brave and original as knowing the latest underground indie flick.
The posthipster believes creativity is not limited to a certain subgroup. The posthipster does not define himself by how he is different than the mainstream, but is guided by his individual tastes; he might have a playlist that features both top 10 music and obscure bands; he will not discriminate against fast food or chain stores, nor will he attach a romantic idea to thrift shops and mom and pop places. He might enjoy football on sunday afternoon and read a novel at night. Everything is judged by its own merit, and that judgment is entirely subjective.
Posthipsterism and Poshipsterist theory suggest that culturally there is no such thing as a guilty pleasure; pretending to not like something because you're worried it's too mainstream is just hipster bullshit.