Mark Hamill is Hollywood royalty at this point, especially with Star Wars making a comeback, and Luke Skywalker likely to play a huge part in the story of The Force Awakens.
So, just imagine how you would feel if you met Hamill while he was dressed up as a stormtrooper. In Hollywood. I think I’d lose my shit, personally.
The only problem is that these people didn’t know they were meeting Mark Hamill. Instead, they thought they were just talking to some random guy dressed up as a stormtrooper.
Hamill did this stunt to promote Star Wars: Force for Change, which is a charitable organization keen to give away tickets to the premiere of The Force Awakens. If you donate money first, of course.