Every geek should be able to give the Vulcan "Live long and prosper" hand signal from Star Trek.
A true geek must be able to carry on a conversation using only Monty Python quotes.
A romantic geek can say "I love you" in binary.
I would say additionally that you must be able to say at least a few words in Klingon, have had heated arguments - or maybe even lost friendships - over the Mac vs. PC debate, the vi vs. emacs, or the Android vs. iPhone debates.
Generally to be a geek is to take things that are basically irrelevant far far too seriously. (guilty as charged.)