i dont know if anybody will back me on this, but, i personally see the "how did you do that" as a sub-par performance.
That raises an eyebrow here...
I can remember sitting through one of Mac King's shows in Las Vegas, right next to this older couple. I can also remember hearing that same couple muttering to themselves "wait, how did he just do that?" And as far as I can remember, Mac King has NEVER put on a sub-par performance since being in Las Vegas. As a matter of fact, he probably has one of the best magic shows out there...
If I remember correctly, even Mr. David Blaine himself had quite a few "How did you do that" reactions as well.
We can try all we want to, but we can no longer think like laymen. We no longer respond with "how did you do that" to an effect that fools us. Rather, we tend to laugh or curse...or do a laughing curse. We also ask the fellow magi to "wait, show me that one more time?" And guess what? The magi will. Because we are magicians too. And then we will buy the book or DVD that shows us how it was done and then we will do it for someone else who will then say, "How did you do that."
Laymen don't really know what to say when they get their minds blown away. "Do that again", "How did you do that", "No WAY", "Shut your damn mouth" are just some of the few responses we SHOULD be getting. If not, then maybe it wasn't that good of a performance.
As far as WHAT to say? I am a big fan of not using the same one-liner over and over to different people. Why? Because different people will react differently to the same line you try to use on them. Hell, even the "David Blaine-silent treatment" can make you look just plain rude. Especially if you aren't portraying the character of someone who speaks very little. For anyone who talks a lot, jokes with their spectators a lot and carries on mindless conversation full of one-liners and sight gags, I say not to get all mysterious and spooky when someone asks, "How did you do that". Why? Because it will just make you look like an idiot.
I am a firm believer in playing out the part all the way through. So that means you need to analyze the character you have created, and figure out what HE/SHE would say, not what YOU would say. This in turn will help you create your OWN one-liners and sight gags that you can have in your arsenal.
When someone asks me how I did an effect...I flat out tell them. Start to finish until they tell me to shut up. I mean I use all the terms and everything. "Oh, well see, what I did was culled your card to the bottom and then used an original sleight called the ClipSpin Control to bring the card to the top. See, THEN I utilized a side steal..." etc etc. They end up so confused that they tell me nevermind. 9 times out of 10, they don't ask me when they see me again.
Either that, or I leave them with something sooooo random, they leave scratching their heads at both my magic as well as what I just told them. Something like, "Well sir/maam, all I can say is: A can of Tuna Fish, some double stick tape and Season 6 of The Cosby Show." Once again, they tend not to be repeat askers.
Mike