To start things off, get a coin and place it in your pocket or ask the crowd for a coin. Now go ahead and place your left hand and make it touch your left shoulder. While this is happening, take the coin out and hold it in your right hand and start rubbing it on your left elbow.
Now do a fake move and drop the coin onto the floor. You can try and act very surprised when this happens, just so it looks like you didn’t plan to do this in the first place.
Once the coin is on the floor go on and pick it up with your right hand. While the crowd if laughing at your accident, you need to go ahead and make the switch which will seal the deed. Carefully reach down with your left hand and pick up the coin despite you moving your right hand as if you were going to pick it up with that hand. This switch in hands and coin pick up off the floor is where the trick is done.
Now start rubbing your elbow with your right hand again. While this is happening move your left hand into your shirts collar and drop the coin in there. With everyone focused on looking at your right hand they won’t actually notice you dropping the coin down your shirt with the left.
Once you have dropped the coin in your shirt, go ahead and do some theatrics as you look to get amazed that the coin has disappeared from your right hand. Depending on how convincing you are, the crowd will end up getting amazed by your skills.