I don't think I've ever encountered one of these "hipster nerds".
"Geek culture" is so large and diverse, how can someone even begin to identify an outsider?
I have always liked dragons, I filled my room with dragons, bought dragon toys, read books about dragons, when How to Train your Dragon created a giant following of people who like Toothless, I didn't go "I liked dragons before dragons were cool, you only started liking dragons when this movie came out, therefore you're not a true dragon fan!" I went "Oh cool! More dragons! More people to share my enthusiasm for dragons with!"
Likewise, I've only very recently been introduced to the board game scene at my local comic book shop, I was not shunned for my lack of knowledge in everything board game related, they welcomed me with open arms and were more than happy to explain how to play.
The "culture" is so large IMO, it would be impossible to be involved in every facet of it, so how do we identify someone as a "poser" when maybe they're just an anime geek rather than a tabletop geek?
While I don't believe I've ever encountered a "hipster nerd", I have encountered a rare few people who felt the need to quiz me, but that gets into "fake gamer girls" territory and we've been down that road before.
I don't understand why someone should ever be opposed to the mainstreaming of "geek culture", for me, it encourages more people to love the things I love and that gives us a conversation topic when I'm talking to people I don't know well. When in doubt, I'm sure we can have some kind of conversation about the Marvel Cinematic Universe, Game of Thrones or Zombies.
Also from a slightly selfish angle, more people loving the things I love = more companies making the things I love = more to love.