There are things you don't think about until you spend 2 weeks in a 5 star hotel.
In 5 star hotels you have a minibar that you're not supposed to open unless you want to be charged something stupid like 10 euros for 25cl of still water claiming to have been bottled in the opposite side of the world from where the hotel is located.
But on top of the minibar there are glasses you can use for drinking, and an ice bucket you can refill in the corridor. This allows you to put ice in tap water. If the tap water is undrinkable, buy a 3l water bottle in the nearby supermarket and use the ice to make it colder without upsetting the minibar.
Note: this specific minibar has sensors, and charges you the very moment you take things away from the fridge, so it's out of the question to temporarily empty it to put my things in for a while.
Now, the ice bucket, the ice clips in the ice bucket and the glasses used for drinking, how do they clean them? Are they sent 6 floors downstairs to the dishwasher? Certainly not.
They use the DETERGENT FOR THE WINDOWS.
I went to get some ice and realised that the inside of the bucket (and the ice clip to put the ice in your cocktails) smelled like window detergent. Then I sniffed around: same did the glasses, and one had leftover foam in the bottom. So I had to wash the toxic stuff away from them before using them.
Now I can assume that I have to wash the glasses every time I need them, as I know that they are not necessarily cleaned with food-safe detergents.
So, here's the tip: before leaving the room in the morning, I put glasses and ice bucket back on the tray on top of the fridge, and I put the cheap-pretending-to-be-fancy cocktail mixing plastic sticks back in the glasses.
This succeeded in tricking the cleaning people into believing that I didn't use them. As a consequence they didn't clean them, and now I can use them without needing to wash the window detergent away first.
Another tip: don't leave your shoes next to the sofa, or the cleaning staff will put them on the sofa when cleaning (sometimes they forget them on the sofa, so you realise). Even better: don't put them next to the bed.
Another tip: if the breakfast buffet has only scary things it takes half a day to digest, make friend with the omelette cook.