Disney is the happiest place on Earth. For the most part. It can be a little less happy if you're parent of four and you just spent your mortgage payment on lunch. Part of the magic is all of the characters that walk around the park. Seeing Mickey in the flesh is like living in a real life cartoon. The only other way to get that feeling is to do mushrooms.
Obviously with a lot of families around you have to watch what you wear at the park. You can't bust out your metal band t-shirt with the dragon dismembering a topless lady on it. This guy was just trying to show his support for his favorite DJ (Deadmau5, pronounced dead mouse), but failed to realize how Minnie and Mickey might perceive it. You can see Minnie's obvious dismay. Even through that emotionless mask we can see the pain in coming to terms with her mortality.