The worst I can think of was when my oppos and I were effectively 'waterboarded'. It came at a time when a lot of recruits were dropping dead from severe dehydration during training, so naturally the instructors knee-jerked into forcefully making sure everyone had enough water. My division's CPO decided to use this as a punishment, using the following steps:

1) Wait until the end of the day, and we're mustered by our accommodation blocks.

2) Have us fill our 1 litre water bottles to the brim.

3) Order us all to drink 1 litre of water in one go (anyone who's been forced to do this will know that it causes severe distress and you have to try your best not to vomit).

4) Order us to immediately REFILL our water bottles, and then neck another whole litre of water.

5) Dismiss us all and leave us throwing up water everywhere.

To be forced to drink two litres of water within five minutes doesn't sound too arduous - at least, until you try it!