In the last post you implied that jily fell for each other the moment they met, why do you think this? I never really got that vibe (it seems like they both like each from atleast as early as their 5th year) but I could be missing something here.

thank you very much for the ask, anon!

for the simple reason that both lily and james choosing to be so bothered by each other the second they properly meet is a very good sign that each considered the other to mean something significant to them from the off.

after all, if lily considered james to be completely uninteresting and unworthy of her time... then she wouldn't have involved herself in the dick-measuring contest he, snape, and sirius get into on the hogwarts express. and james wouldn't have felt compelled to be rude about her - in a way, let's be clear, which he intends her to hear and to know is directed at her - while she's storming out of the compartment with her nose in the air if he didn't think she was worthy of his attention either.

this doesn't mean that what each of them felt for each other was immediately romantic [after all, they're eleven...], but that sort of prickly, "no, obviously i don't care about james potter! i hate james potter! he annoys me just by breathing!" dislike of someone can [in many cases] be a precursor to love...

[because - of course - the opposite of love isn't hatred... it's indifference.]

and it also doesn't negate the fact that both snape and sirius are directly involved in starting - and maintaining, and escalating - the beef. snape's immediate dislike of james and sirius [and their immediate dislike of him] has that same sense of only being so bothered by someone because they matter to you. the text points this out explicitly - that snape is immediately jealous of james having the "indefinable air of having been well-cared-for, even adored, that snape so conspicuously lacked".

and that james is immediately jealous of snape having lily.

one of snape's great tragedies is that he doesn't quite possess the ability to understand the subtext of lily's relationship with james prior to the breakdown of their friendship - and that this is why james and lily bantering [pretty flirtatiously, to be frank] while james is bullying him blindsides him, making him so angry that he lashes out in the only way he believes could soothe his pain and calls her a mudblood.

it's clear from the princes tale, for instance - especially the bit where they're arguing about mulciber versus the marauders - that snape is trying to needle lily into stating conclusively that james doesn't matter to her [and that he's immensely reassured when she seems to does so], but that he doesn't realise that lily calling james an "arrogant toerag" doesn't actually indicate the indifference he's looking for...

that conversation seems to take place in their fifth year - and snape being worried that james' interest in lily is sexual might very well have only started then - but it has as an undercurrent the heavy implication that snape and lily have had similar discussions before. it seems pretty unlikely, for example, that lily would ask snape "why are you so obsessed with them?" if he'd only just started bringing james and his cronies up with her - and it seems equally unlikely that snape would have felt the need to complain to lily about the marauders prior to this conversation if he hadn't been worried for a significant amount of time that lily was not quite as unconcerned by james as she claimed...

[this - for what it's worth - is why i think the anti-jily "james forced her into being with him!" argument doesn't hold up. james' technique is pretty heavy-handed - absolutely - but he behaves the way he does because he's noticed that lily not only reacts to it, but that she reacts to it in ways which aren't boredom, sadness, or fear. and she does this - of course - because james sincerely interests her.]

and - while this comes with the risk of undermining what i said yesterday - it's striking that this is exactly what happens with ron and hermione. while their friendship establishes itself very differently to james and lily's - and while the course it takes towards romance is also very different - that same "no of course i don't care!" interest in each other is present from the get-go.

i don't think this is because jily and romione are intended by the doylist text to be parallels so much as i think that it's a way of conducting interpersonal relationships that jkr is clearly fond of in her own life [which is due both to her own personal idiosyncrasies and the cultural context in which she lives - insulting people you care about is the british love-language, describing a man as an "arrogant toerag" is practically writing him romantic poetry].

but i do think the fact that it turns up in how both couples are written - particularly since the doylist text thinks that james and lily were a perfect couple, even if its readers disagree - is intended to show that, in both cases, the fact that it was irritation-at-first-sight meant it later turning into true love was inevitable...