If all else fails, you can just pretend that the screw-up was actually the way the trick was supposed to happen or say something about needing to take the trick to the repair shop. These won't work most of the time, but if you're around a comfortable audience of friends, it just may get a laugh or two. WARNING: never do this around a group of people you just met unless you're doing comedy magic. They will be disinterested in the rest of your show and will only focus on the fault.

If your working with a semi-serious audience you could say in a very unconvincing angry tone "Well if your gonna mess it up like that and not even work with me a little it'll never work". Then just move on.

another thing you could do when you mess up is say something like, "see that egg on my face? gosh, that was a big chicken or something like that

i agree

I would really be careful where you say silly remarks like this. I only say these things around my friends. I've tried it on different audience and i only get simpathy laughs or stares that seem to say "Wow, you're terrible"

Here is something I do if I screw up a double: Suppose I do a convincing double. Now I need to replace it (turn it back face down). Because I do the Daley Strike Double, which means that I do not use a get ready, sometimes I will grab the wrong number of cards. Once in a great while I will turn back over three instead of two . Now I have an indifferent card facing up--in a face down deck--oops. What I will do (this has happened twice) is I will say to the card, "what are you doing here?" Then I will grab it and fling it accross the room and go on with the trick. Surprisingly, most people laugh and go back to watching the trick, none the wiser.

hit them over the head with something heavy and run.....