[This is where Sebastian wants to deliberately misunderstand and say something like "Oh? Do I typically address you as something else than 'sir'~~?", but well, event...]
I employ it when the present company demands it, of course, but that is not the case here. [Because Lucifer is hardly royalty.]
Here, I use excess formality in place of aggression, since the situation hardly should escalate. I don't suppose you are familiar with sarcasm, at that?
[...Okay. He didn't mean to be straightforward. This time Sebastian forgoes the puzzled look and doesn't comment on how strange this is, but his smile, if one pays attention, stiffens somewhat.]