The more Trek shows and films you vehemently hate, the better Trekkie status you achieve. As long as you regard one of them as the one and only true Trek that follows Gene's vision (preferably The Original Series or The Next Generation, but with enough passion anything will do, really). It is also a neat trick to avoid having to watch more than one.
Develop some selective amnesia - conveniently forget any episodes of your favourite series that weren't any good, and never acknowledge their existence. IMDB is also a nice source of Trekkieness. Pick the episode of any series rated in the top 10, and start a thread slamming it as overrated and not really that good. That gives you bonus points that fire you directly into Trekkiehood.
Oh, you mean a trekkie like someone who actually enjoys Star Trek? How quaint. It's a rare thing these days.