I've never been on a U-boat before...

But it couldn't be any worse than this. I had numerous other complaints but I'll just do the worst one.
We paid 20 euro/person for the buffet. Service was terrible - it took 15 minutes before a waiter even approached our table, just so we could have water with our meal. On the way out of the restaurant, the waiter told us to pay about 6 euros for the water. I pulled out my wallet, stating that I was unaware that there was a charge. He dismissed us, saying we didn't have to pay, I offered to pay TWICE more and he said we didn't have to.
An hour or so later, this woman in ship's uniform knocks on our cabin door (I was in the lounge) and my wife literally has to get out of the shower, wearing a towel, to answer. This woman, without telling her name or position, starts demanding 6 euros and arguing with my wife. After being told that I am in the lounge, the uniformed woman approaches me in the lounge, demands the money and basically calls me a liar in front of all of the other patrons.