I tried looking for it and I found a YouTube video of some Indian street vendor doing it, but iirc my old video had been of some British guy. There's more than one apparently.

The loss of sensitivity doesn't happen all at once, plenty of cooks and serving staff have much higher tolerances than non-cooks/waiters. I'd expect that this is at least partly from damaged nerves, but while they have reduced sensitivity, iirc then the British guy said that he had lost all sensation in his hands.