I do think it's interesting how Meng Yao doesn't use his Customer Service Face with Nie Mingjue ever while he's in Qinghe. He uses it with the captain, of course:
He's a little more subdued earlier when he's talking with everyone at Chang Manor--he looks pleasant and disarming (which makes sense, given that these people don't know him and he doesn't want to look like he's talking over Nie Huaisang, who should technically be the authority there on his brother's behalf), but it's not quite so forced.
But when he's actually interacting with Nie Mingjue on the clock, he's neutral to almost stern.
Even when he's trying to convince him to change his mind about something (obliterating Xue Yang on the spot, in this case), he talks to him... not quite as an equal, exactly, but as an adult.
And when Nie Mingjue ultimately agrees with him, he doesn't fawn or thank him or anything, he just gives this businesslike bow of assent.
And politely but firmly orders two guards over himself to help him escort Xue Yang to prison.
...and then once he leaves the building (and Nie Mingjue's field of vision) he encounters the captain and immediately goes into his Customer Service Mode, with his smile getting wider and more strained the more the captain disrespects him.
I just think it's interesting! I'm not necessarily arguing that the way he interacts with Nie Mingjue is his natural way of being; it's possible that Meng Yao simply clocked that Nie Mingjue values plain-spoken competence and adjusted his mannerisms accordingly.
But if this directness is what Nie Mingjue was accustomed to seeing from Meng Yao, imagine how unsettling he must find the obsequious rictus smile that Jin Guangyao wears 24/7 in his father's service.
