For me, "fred" is synonymous with "really uncool" and I would describe a fred as someone wearing ill fitting, low end clothing, possibly a mirror somewhere, visor helmet, mountain bike pedals on a road bike, and misplaced accessories. Clip on aero bars with a rider more upright than I am on the tops of my bars, and going 15mph on flats is maybe the most fred thing I can think of. Basically anyone who buys every accessory and none of it makes sense is a fred.
Cliff's notes: walk into performance bike and you'll immediately be able to define "fred".