One of my costuming pet-peeves is when someones has spent obvious time on their outfit, but doesn't even really true to get the hair right. I realize that sometimes we run out of time, or money, or energy, or our wigs get lost in the mail or end up the wrong color, but it just makes me so sad for the costumer. They got so close only to miss out on one of the most important parts about overall character appearance. This especially irks me when someone has long, straight, unshaped hair, and thinks it will work for any long haired character regardless of style. 9 times out of 10, our real hair just doesn't have the volume or shape of these crazy characters we adore, at least not without a lot of work.
Another pet-peeve is when people spend lots of time on making a costume but didn't bother to make sure it would actually fit them. So they have a costume that they spent lots of time and energy on, but it looks cheap and thrown together. It makes me sad.