A hand I had accidentally dumped boiling liquid over, although the reduction in pain wasn't complete in that case, and it was difficult to maintain concentration. (I couldn't make my attention... large enough? To encompass the entire hand.)

I don't generally apply the technique, because it's usually counterproductive; the problem with pain is that it is distracting me from what I want to pay attention to, so giving it my full attention is just making the problem worse.