This thread could be as long as a piece of string. Pretty much anything that is non-standard fitment to a vehicle without an engineers certificate is deemed a defect. Most of the time it's just the mood the officer is in that will govern the amount of things he finds. But in keeping with the thread some I've seen are.. too low, too wider wheels, wearing a harness, sharp corners on front mounted intercooler, roll cage, no cat, too loud, gauges on dash, chromed mirrors, NOS etc etc.