The best time to execute a difficult sleight or move is when your audience is laughing. That way they won't be focused intently on your hands and such. If they were, you probably wouldn't want to do magic for them anyway. Here are some phrases that I've found helpful:
-"Everyone has a photographic memory. Some just don't have film."
-"How many of you believe in telekenesis? Raise my hand." (slowly lift up your arm with a horrified look on your face)
-"You're just jealous because the voices are talking to me and not you!"
Heckler: Just tell me how you did it. Come on...
Magician: Can you keep a secret? Good, so can I!
Heckler: I know how you did that!
Magician: Man, if I lost a dollar for every time they were wrong, I'd be performing for my pet gerbil under a bridge somehwere...
-"Multitasking means screwing up several things at once."
-"Support you're right to bare arms!"
(roll up your sleeves if you can as you say this)
-"I dont suffer from insanity. I enjoy every minute of it!"
- (after rubbing your hands together or something similar) "I hate friction. It's such a drag."
-(In your best Arnold voice)"Before this vanished it said one last thing to me: I'll be back" (works best if you can make the object reappear.)
-"A little nonsense now and then is relished by the wisest men..."
-(Best post-pickpocketing line) "I've got what it takes to take what you've got."
-"You guys wanna see a trick or a miracle? What do I look like, Moses? The only thing I can divide in half is this (use with a multiplying objects routine)
Like I said before, if you have to grab something out of your pocket, or do a switch, or any other sleight, what better time to do it then when someone is throwing their head back in laughter? Plus, it takes a little pressure off of Mr. Miracle, ya know? I hope these will help you, just as all these forums have helped me. Good luck with all of your performances