A Trekker wears a starfleet uniform to a convention
because it's fun.

A Trekkie wears a starfleet uniform to a convention
because s/he has heard that it is in style at the academy.

A Trekker has a Starfleet Academy window sticker on his car.

A Trekkie is cramming for the entrance exams.

A Trekker meets Marina Sirtis/Gates McFadden at a convention,
tells her how pretty he thinks she is,
that it is too bad she is married or he would ask her out.

A Trekkie meets Deanna Troi/Dr. Crusher at a convention,
tells her how pretty he thinks she is,
and asks her if she is still seeing Riker
(Picard, some alien patient, et al).

A Trekker loves watching the show,
nitpicking and discussing it with friends.

A Trekkie loves watching those documentaries filmed aboard the Enterprise.

A Trekker thinks Wil Wheaton was a lucky kid, who got to play a kid on Star Trek.
A Trekkie thinks that Wesley Crusher was a lucky kid who got to sit on the bridge.

A Trekker thinks that it is a shame that the show is coming to an end.
A Trekkie thinks that it is a shame that the crew is being reassigned and the Enterprise is being decomissioned.

A Trekker knows that there are gaping holes in the technology,
but ignores them and enjoys the show.
A Trekkie can't wait for the price to come down on those home food replicator units.

A Trekker buys pips for the rank s/he wants to be.
A Trekkie wonders why he is constantly passed over for promotion.

A Trekker tells his/her new girl/boyfriend that s/he really likes Star Trek.
A Trekkie's new girl/boyfriend is an underclassman at the academy.

A Trekker wonders what sex in zero g would be like.
A Trekkie wonders what sex would be like.