My favorite reactions are a kind of .. stunned silence? During my Transference routine, in the beginning, there's a part where everyone makes the same expression. It's a sort of confused, "What wait's going on", "I'm not doing that!" reaction that I love and I even point it out now, because everyone makes the same face.
Other than that I generally always get a lot of joy out of the "intake of breath, stunned silence" reaction that many of my routines evoke. I rarely go for the shouting-running-around reactions.
I will also say one of my absolutely favorite reactions came not from my show, but a show I was doing with my fiancee this past June. We do a partner side show act, and she has recently taken over doing the Animal Trap. She largely uses the script I came up with, which was honed over many performances, but she is slowly making it her own. Anyway, there's a lot of build up, with multiple instances of seeming like one is going to put their hand into the trap only to stop and make a comment of some sort. It's great fun. She was doing it at one show, and as she actually popped her hand into the trap, a guy in the back just shouts, "Oh S&$%~!!!"
It was so out of the blue and genuine I literally started laughing out loud and had to walk away and take a moment to calm myself down. Absolutely hilarious. He actually came up to us a little later after the show and explained he was sorry, but he thought she was actually going to set the trap off and somehow get her hand clear of the jaws before they closed and actually just letting it close on her hand was completely shocking.
