The attire for a Costumed Nerd is perfectly intuitive.
In this case, a particular sci-fi (or other nerd-type) character strikes a chord with the Costumed Nerd, prompting them to go to great lengths to support and even honor said character. Imitation being the sincerest form of flattery, the obvious way to express this undying support is to duplicate the clothing that adorns the character.
It is this nerd's hope that the Costumed Nerd chooses opportune times to cloth his or her self as their favorite character, such as conventions, conferences and Halloween, but that is not always the case. A few, extreme Costumed Nerds will take it to the next level, outfitting themselves in science fiction costumes in their daily lives.
Enough narration. This attire can only be done true justice via digital imagery.