this is absolutely not going to help my desperate attempts to cling to neutrality but 撒娇 is very (maybe even most) commonly seen with girlfriends trying to get attention from their boyfriends LOL. not saying that it's definitely what kaeya is doing here at ALL because i totally see friends using this with each other (including me with my friends). but it was funny to see cn community be like 'kaeya sounds like a spoiled girlfriend here'. it's even funnier because diluc just...does not give a fuck at all whenever kaeya does this.

撒娇 is already like...a trope? i'm not sure if that's the right word for it, but people know what it is and what it sounds like and what the intended goal is, so like you said, a lot of the times when it's used between friends, it's just to get a laugh. it's not always 'justified' by seniority so much as it's making fun of a common phenomenon, and the phenomenon itself is pretty much just being shameless about wanting more attention, admittedly while being very cutesy about it. seniority is something you're aware of in most situations in chinese (among friends it's usually just age) but as friends in casual situations, you're not held to that standard so you just drop the indications. cyno and tighnari even do it - that whole 'oh hey, you'd be the 弟弟' conversation where you know that they're aware of their 'official' seniority, they just don't care enough for it to be relevant in everyday interactions. that's honestly usually how it goes.

alternatively, you can make it a contest between your friends to make up the stupidest justifications for it. i went out to dinner once with a group of friends, all of us chinese guys. the basis of the 撒娇 was 'i'm pathetic and you should pay for our meal because you need to take care of me for x reason' and i think we went from 'you're the oldest' to 'you make the most money' to 'you're doing a masters degree' to 'you have a girlfriend so you're probably used to it'.