I know the feeling very well indeed. For me I'm still trying to get over it but I've found the only way to do it is just throw yourself at it like any fear, and ultimately see that it doesn't hurt you really.
For me I guess my biggest fear is that my ego might come away slightly bruised or somethin as it may not go as well as in my head, or they may just not like that trick so much and I won't come off as Mr Cat the amazing. I love doing a few tricks and just having a laugh but there's always a bit of you that wants it to be perfect every time, especialy when it comes to strangers. That and ironically paranoia that my nerves will cause me to totally gash up a trick I can do so well in rehearsal on my floor at home with my cat.
So I've just taken any small impule when it's come, forced myself to jump on it when I've been out and gone up to someone and asked if they fancied seeing a trick as soon as it was apt. I find that being prepared in your head is a question of how long would it take you at home or with yoru best mate when asked off the cuff, try and put yourself in that place, take a moment to answer and then say 'sure I'll show you something'

Doesn't matter if you trash it totally, you may be embaressed or whatever but other people will respect you for doing something they wouldn't dare no matter how it goes.
I found this link on my travels the other day, it's a book by this cool looking magician dude, I don't think it's out yet but he's big into his 'getting out there and being confident' training. You might want to take a look. I'm certainly curious. My adrenaline still goes a bit mental even when I'm at a gathering round a friends house...but the more I do it anyway the easier it becomes.
The random 'get out there' guyHope that's of some help! Cheers
