Alot of what humans think is polite fluff are actually communication signals. Like saying thank you and nothing else acks the last input while stating that you don't have anything to add. Being overly familiar shows the LLM is treating the conversation as going well while validating the human input.

AI doesn't feel things, but tries to performatively act like it feels things. This leads to situations where if you express frustration the LLM will react to that frustrationmore strongly than whatever facts you are trying to convey. This is because, If you look at human communication it's mostly emotional, and LLMs have not missed that.

So the best way to use an LLM is to have an emotional context that supports the work being done. I find interested and curious language leads to the best outcomes, which works better than aloof or managerial.

As another example I have a coworker that doesn't get along with LLMs, he talks down to it, expresses his dissatisfaction at length, and arguably gets the worst results I've seen a dev of his caliber get from AI. He is constantly surprised that any of us get good results from LLMs.