Ritual and highly visible humiliation became a televised fad, I believe, when Japanese game shows such as Takashi's Castle started showing on Western TV. We now see American equivalents regularly, where contestants often injure themselves trying to negotiate obstacle courses. The American series, Jackass, involved people actually injuring themselves. It evolved into two movies.
Now the combination of YouTube and smartphones has made it easy for people to debase themselves with vigour.
Perhaps it's experiencing the idea that we're all equal in moments of extreme adversity, when the ice blocks smash into your spine. Perhaps some of us are addicted to shocks. But I think it's more likely that it's a combination of a feeling of being extremely liberating and demonstrating your competitive machismo. Ritual humiliation carries respect.
However, it is unfortunate in New Zealand culture that drinking somehow has to work its way into the situation, as another way to demonstrate how "macho" you are. My view is, one intense extreme is probably good for you. But don't drink and ice.