You cannot tickle yourself but you can cause yourself pain. Why the difference?
In your Christmas special you talked about why you can't tickle yourself because the brain switches it off while you perform the conscious tickle. Why can't you do the same with pain? If I stick a pin in my finger after telling myself it's not going to hurt, it still hurts?
Actually you can tickle yourself and Sarah Jane Blakemore did some nice experiments showing how you can do this. What you have to do is get a tickle stick, and when you move it, it has a delay. So from your movement there's a pause between actually when the thing does a tickle on you. You find that that will actually make you laugh. She did some experiments to show why that is. In terms of the pain bit, if you do prepare and block yourself you can boost those endogenous opioids just like in that fight or flight response or in the placebo effect. When you know the pain's coming and you psyche yourself up for it you can actually just take the edge of it and modulate that pain a little bit.