This reminds me of something I only noticed on rewatch. In the first episode, Zhao Yunlan tells some random police personnel to call him xiao-Zhao (little Zhao). But he's likely older than them and also outranks them, so if he wants to be friendly with them using "lao" (old) is more suitable? I'm thinking since his dad is also in the same line of work, his dad would be "lao-Zhao" and therefore Zhao Yunlan refers to himself as "xiao-Zhao" when talking to people in the police force, regardless of seniority. Though, of course, the baby police here don't call him that and use Chief Zhao instead.

And then in episode 8 he calls up the university and straights up introduces himself as Shen Wei's good friend, xiao-Zhao. I can't say for sure where on the etiquette scale this falls on but I'm guessing it's at least a little inappropriate. Considering the image Shen Wei is likely to have at the university, just imagine the rumour mill after that call.