Small plot hole regarding "the matter of the bill..."
Why did Chef ask his patrons to pay for their meal at the end of the night? There's literally no reason behind it, except because it's part of the "experience..." but given the fact that Chef was planning to kill all his patrons, the staff, and himself, there's literally no point to asking for people to pay for their "meal," if you could call it that, as Chef Slowik had no intention of living through the night. He's basically just "going through the motions" in asking his patrons to close out their bill. He won't be there to enjoy the economic benefit to having his guests PAY for their food, so why bother doing it at all? Did it make for a funny scene in this dark comedy? Sure... But has no effect on the plot whatsoever. Does it show he's crazy? Sure... But we already knew that from prior scenes... I still loved the movie, I just found that bit to be trite, and essentially confirms that not only is everything Chef believed in for nothing, but he won't even be around to enjoy putting his guests in their places once and for all.
Just thought I'd point that out. Still a great movie... But I found that one scene to be totally pointless, save for being a polite adieu coming from a man who truly didn't care anymore about serving the customer well. Know what I mean?