The risks are low, very low if you have a GFCI but if the conditions are just "right", it can be lethal. It a enough current goes through your heart at exactly

The risks are low, very low if you have a GFCI but if the conditions are just "right", it can be lethal. It a enough current goes through your heart at exactly the wrong time, it can mess with your heartbeat and cause fibrillation, and without help, you die. It is a game of Russian roulette. There are much more than 6 chambers, but the bullet is there. If enough kids do this stupid challenge, there will be deaths.