This guest in the most unorganized person I ever met, incapable of following simple instructions, threatening me in chat.
The thing is that I make a flexible check-in policy by using a combo lock and leaving the key inside. Guess what - this guest TOOK THE KEY WITH HIM and not just making it very challenging for the next guest to get in and out of the building, but he DENIES it and refuses to reimburse the cost of getting a new one. And, as a retaliation to my reasonable request to pay for the key knob, the guest requested money for "cleaning" while the place was clean before them by all possibly knows standards.
Unbelievably bad experience with this person.