For the record, my typical daily attire is usually shorts and a t-shirt (being retired helps with this). The shorts are of the nice "casual variety" and the t-shirts are presentable. I have a few sleeveless shirts I wear to the pool or around the house. If we're going out to eat, where determines whether I wear a collared shirt. For most, it's a collared shirt. I do wear long pants when I play gigs with bands and sometimes even a tux.
When we go to WDW I wear shorts and a collared shirt, sometimes a Disney-themed t-shirt if I know we won't be eating at a table service restaurant. There are always exceptions, but I try to be presentable. The one issue that I never make an exception for is hat is off at any table, indoors or out. That's just the old fart in me.
I believe the only restaurant at WDW that still requires a jacket and tie is Victoria and Alberts. We used to enjoy Broadway at the Top, the Gulf Coast Room, and the Empress Room, but I guess there just weren't enough visiters who were willing to get dressed so they are now the California Grill (Broadway at the Top), gone (Gulf Coast) and Fulton's Crab House (Empress Room). Of course, the fine dining is also gone from all three.