Biggest pet peeve for me is axle slip, which I've had in the past with Indy, Ace, and Thunders, and any kind of crease or air bubble in the grip. If I'm in a rush gripping a board, air bubbles are always easier to deal with, but creases are the worst.
Things I don't like seeing on other peoples setups, which is ridiculous because I don't have to deal with, are Grizzly grip, Shake Junt grip, colored wheels, and colored trucks, but I'm a simpleton.