"Think of this as a giant illusion on a minature scale. A freely chosen coin visibly penetrates a sheet of rubber tied over the mouth of a glass. You can watch this in uber close up and STILL not see the secret. I showed this to Cameron Francis on his last trip to the UK, and he COULD NOT work it out. He got really mad. It was funny!"
Gather your friends around a nice tall glass of water, they'll need a refresher after this astonishing trick! Wrap a solid piece of rubber over the glass's mouth and 'plunk' drop a solid quarter straight through it. Let them examine the glass, rubber, and quarter all they like; they'll only come away even more impressed with your dizzying magical skills. Instructions included.