I'm pretty new to magic (I've been doing it a few years), but the other day I got a reaction from some friends I could've only wished for.
We were just spending some time together, hanging out over the last weekend. We had just seen a movie and as we were sitting outside the theatre talking, I asked if they wanted to see something. They know I usually have a pack of cards with me, so when I pulled them out of my pocket they knew what to expect. I then proceeded to do the trick where the spectator picks a card by cutting the deck, writes the card's name down a piece of paper, watches the paper burn, and then watches as the name of their card appears on your arm after rubbing the ashes all over it (sorry, I don't know the official name). Anyway, after they cut the deck I started talking about how what I was about to do was based on a principle of Voodoo, reading signs from the spirit world and what not. I told them I'd seen this done before, but had never actually had it work myself. Then I finished the trick and acted as stunned as they were. But what really made their reactions great, was that they believed it all came from a spirit. They were actually afraid of what I'd just done.
It was all I could do to keep from laughing. They've been talking to everyone they know now about the "scary" incident. I just hope people don't start thinking I worship Satan or something.
Anyway, have you ever had spectators react in a way that went beyond anything you were hoping for?