4. July 4th
This is another one of the busiest days at Disney World, with theme parks sometimes reaching full capacity, which means closing the parks to further admittance, at least temporarily. If you have fast pass or dinner reservations, or are a Disney Resort Hotel guest, you will be able to enter, but the crowds will be exceptionally heavy. I would suggest that when a particular park has reached full capacity, go chill somewhere and return later for the spectacular 4th of July Fireworks Extravaganza.