The hallmark of nerd fashion is practicality.  Not the sort of practicality that thinks, “I’m going to be on my feet most of the day.  I think I’ll wear my Cole Haan flats instead of my Christian Louboutin heels.”  It’s practicality mixed with overthinking.  As in black is elegant + white goes with everything = Amy dresses like the help at her aunt’s fancy dinner party.  It’s often practicality mixed with overthinking mixed with cheapness with results like this:

It’s early morning.  I’m going rollerblading.   I need the yellow fleece to be visible, but (I think) it’s really cold out this morning so I need a windbreaker.  But the fleece has to be on top for the whole visibility thing.  Of course, I could spend$159 for a warm, high-visibility jacket at REI (and, as a bonus, I could apparently zip things into my armpits):

But I’m a nerd!  Why on earth would I spend $159 when I have the ingredients for a perfectly practical solution?