Term used in reference to a group of stereotypical, postmodern hippy-wannabes.
Not to be confused with true, original, peaceful hippies of the 1960s, this modern day self-proclaimed socially conscious group often have extremely aggressive, militant views and attitudes, and will resort to physical measures during the course of their unwarranted, misdirected "peaceful protests".
Readily identified by their stereotypical, common choice of footware (see, Birkenstocks), members of this social classification can be found wherever protests are being held, regardless of how valid the cause may be.
see also Hipptards.
QFT (in Berkeley, California):
Birkenstock Gestapo: "A guy who has just moved here from Nigeria and became a US Citizen can't be called an African American because his ancestors weren't slaves."
Birkenstock Gestapo: "Why do you hate so much?"
Me (confused as all hell): "Erm... What are you talking about? Then, *mocking*:Dude, Why don't you stop swimmin' at the bottom of the bong, man."
Birkenstock Gestapo: "Nazi" *snarls*
Me: /facepalm *walks away laughing*