We're going to try and get PS for Thanksgiving dinner, so DD and I are planning on "dressing up" for the Holiday In the Unofficial Guide to Disney, it just states Casual, no Tank Tops
The only rule is no cut-offs or tank tops. There will be people there dressed all different ways; resort casual to a little bit dressier dress. Whatever you are comfortable wearing will be okay. I have seen far more dressier slacks and casual dresses there then shorts, but there are people who wear shorts and tops.