The main things to me atm is clipping. I can put up with it on hair without issue because that's extremely common in games, especially with longer hairstyles.

The one that bugs me is tail clipping that happens when I wear something that includes a cape. For example the ilvl130 BLU gear. It happens to an extent on various skirts, longcoats, and dresses as well but the capes is where it becomes blatently out of place to me.