Anything done with the sole purpose of looking more non-conformist (which, invariably, everyone else is doing):
Not wearing a tie with a suit
Untucked shirts (even worse: untucked shirts under a jacket)
Ugly, tacky ties
Ugly, tacky pocket squares
Over-poofed or Angry Jester stuffed pocket squares
Jackets that are too tight and/or too short
However, I hate it even more when someone artlessly follows the typical iGent prescriptions (wear a pocket square, wear brown shoes, wear a knit tie, make sure you have high armholes, etc.).