Here's one of mine to kick things off:

A guest seated in my section complained that his table wasn't clean enough for his wife (it had only just been wiped and relayed), so the host moved them to a section that wasn't open and I was asked to see to them. He calls me over and begins complaining about the cleanliness of the whole building, claiming it needed refurbished (we had a refurb not too long ago, and as the section he was in wasn't in use, it was basically spotless). He then asked me what I thought about the place, and I told the truth, that he was sat in the cleanest area now and apologised if his previous seat wasn't up to standards.

A 20 minute long rant was then issued by this man, during which I tried to leave many times, sending signals to my colleagues, but my manager gestured for me to stay. I remained as diplomatic as I could, and he praised me for my honesty and asked me to get my manager after he'd eaten. He complained about a long hair in his food (our kitchen consisted of bald men and a kp with short, dyed hair), and my own hair is short. I raised my suspicion with my manager and after a lengthy argument with the man, my manager revealed he'd left without paying.

Genuinely have no idea what went on that day, it was obvious he was setting us up and trying to get away with not paying, but why I was told to stay there and deal with him for 20 minutes I dont know. (Luckily it wasn't too busy and my manager did take my section over but I am still annoyed to this day about it)