Doing my head in – enough of that!
Not really an illusion as such, but do you know the hole in the hand trick? Get an empty toilet roll holder, hold it up to your right eye (as if you were using it as a telescope – I’m not saying that’s what I was doing!) then slowly bring your left hand across the front of the teles-eh, toilet roll holder and it should look like part of your hand has vanished.
Or you can just make a circle shape with your hand.