This is straight from the Cast Hub (So in other words, it's official):
The Walt Disney World® Resort is a heavily themed environment whose world-renowned brand is woven into every element of our show. We reserve the right to exclude from all of our gated attractions (i.e, theme parks, water parks, Downtown Disney® Pleasure Island, DisneyQuest® Indoor Interactive Theme Park) Guests whose appearance could create a distraction to the show. Some examples of Guest appearance that could be considered inappropriate or a distraction to our show include, but are not limited to:
Adult costumes or clothing that can be viewed as a costume (unless worn by a child under the age of 10)
Masks
Easily visible obscene or objectionable language or graphics
Excessively torn clothing
Clothing with objectionable material
Clothing which, by nature, exposes excessive portions of the skin that may be viewed as inappropriate for a family environment (e.g. string bikini tops, bikini bottoms, G-strings, etc.)
Objectionable tattoos
The goal of the Walt Disney World® Resort is to provide a safe, secure environment for our Guests to enjoy the show and our Cast Member to deliver the show. To this end, all theme park guests are required to wear shirts and shoes at all times. Swimsuit tops are allowed when worn with other appropriate garments.
Downtown Disney® Pleasure Island, DisneyQuest® Indoor Interactive Theme Park and our water parks have additional property-specific guidelines related to guest appearance. Based on the brand of entertainment provided at each of these locations, an altered standard of dress might, at times, be considered appropriate.
